Growing up in the Magister's City of Ishana, Trinity was enrolled into the Mage's Guild, being put into the same classes as Konoe A. Mercury and Kazuma Kval. She formed a close friendship with both of them, even though the two never interacted. Trinity excelled in her classes, especially within alchemy and defensive sorcery, and found herself becoming good friends with Konoe's younger sister, Celica A. Mercury.
When the Black Beast rose out of Japan and the country was devastated by a nuclear offensive, Trinity comforted Celica as she lost her father, Shuichiro Ayatsuki, although Konoe did not seem to care. She grew closer to Kazuma, becoming his only friend and expressed a concern that his memories had yet to return to him. In 2106, Konoe was chosen for the honor of becoming one of the Ten Sages, although she expressed a belief that Trinity was more deserving. After the Canonization Ceremony, Trinity and Celica took the newly appointed Nine out to celebrate in the Guild's cafeteria.
There, they met Kazuma, and both Trinity and Celica managed to convince Nine to set with him. The four of them enjoyed lunch together, although Trinity tried her best to make Kazuma comfortable despite Nine's constant insults. When Nine and Celica left, Trinity asked about his memory. She soon noticed that both Celica and Nine stood still watching the television as the news blared that a Japanese survivor had been found, and fell silent until Kazuma suddenly became ill and left.
Nine sensed an unusual force in downtown Ishana, so Trinity, Celica, and Nine went to the area to investigate. They found Kazuma with a deep wound within an alleyway that had been partially destroyed. They offered their help to him, but he rejected it, so the girls escorted him back to his dorm instead.
Two days later, Trinity visited the Great Library and found Kazuma inside it, desperately searching the contents of various books. She came to find him to express her worry over him not attending his classes as of late, and asked what he was trying to uncover in the library. He told her that he was trying to find something that could jog his memory, and he opened her heart to her, speaking the most he had ever said to anyone. Trinity murmured some sympathy, but when Kazuma asked her if she could ask Nine for access to forbidden texts within the Ishanan Cathedral, the young mage refused immediately, but did offer her help if she was capable of doing so.
Later that day, Trinity went to the boy's dorms to talk with Kazuma after being warned by Nine that she had again felt an unusual force at play. At the dorms, Trinity expressed her concern for Kazuma's well-being, and told him that if he was in trouble, she would come rushing to his side.
In the academy's courtyard, Trinity found Kazuma and invited him to a little cafe. She did not disclose that Nine and Celica would also be present, giving the impression that she was asking him on a date. At the cafe, she ordered a white tea and revealed to the boy that she thought he could do with some nice cake to unwind after all he had been through recently. Trinity listened to Celica talk about her failing grades, straining a smile as she heard some of the girl's reasoning.
Eventually, Celica and Nine began to fight over Shuichiro again, and as they slammed their fists into the table, it sent Trinity's tea all over her. She rose from her seat, scaring everyone and she gave them a seemingly endless speech on being kind to one another, and to everyone and everything around them. Kazuma then left, so both Trinity and Nine followed after him.
When they found the boy near the edge of Ishana in the dead of night, the girls asked him why he left. Kazuma came up with the excuse that he was looking for an acquaintance, and verbally hurt Trinity as she expressed sincere concern for his memories. She went back with Nine after she interrogated the boy, still hurt by Kazuma's accusation that she had used tracking sorcery on him.
The following morning, Trinity went with Nine to the boy's dorms after Celica left a letter explaining that she had gone to Japan. Nine was ready to kill Kazuma, suspecting that he was to blame, and it was only with Trinity's reasoning that she was able to get him to be spared from the Sage's wrath. Trinity gave him the letter to look at, and apologized for doubting him. Nine was forced to leave to attend to her duties as one of the Ten Sages, but Trinity stayed to apologize further until she also left.
A few hours later, Trinity waited for Kazuma in the academy's courtyard, and saw him attempt to enter the Cathedral. She stopped him, and he accused her of tracking him, telling her that he had suspected Nine had given the order. This accusation was true, but Trinity did not reveal it. Instead, she begged him to not enter the Cathedral as it was against their laws and grabbed his arm, telling him that she knew he was the reason why Celica left for Japan. She continued to beg him to not enter, saying that he was not acting like the Kazuma she knew. Tears welled up in her eyes, but Kazuma laughed, raised his hand, and unleashed a sorcery shock wave that knocked her into a nearby pillar. The impact immediately sent her into the unconscious.
When Trinity awoke, she was in her dorm room with Nine by her side. The Sage explained the situation and what had happened to her. Instinctively, Trinity asked about Kazuma, and Nine replied that he had entered the Cathedral and disappeared, although there were signs of a struggle. She then promised that she would travel with Nine to find Celica, but in her heart, Trinity desperately hoped to find something in their travels that could tell her about Kazuma's whereabouts.
Nine frantically searched for Celica, and Trinity helped. The two of them tracked her down to Kantō, Japan, finally finding her on a mountain trail with an odd man in a red jacket. She calmly watched as Nine attacked the man and then got into an argument with Celica about running off with strangers. While the sister's were fighting, Trinity brewed some tea and offered it to the man, introducing herself and learning his name - Ragna the Bloodedge. Eventually, Trinity interfered with the quarrel between the siblings, and they settled on a plan to go to the First District. Both Trinity and Ragna bitterly smiled as they watched the two of them initially go in the wrong direction.
While they made their way towards the First District, Trinity cast protective sorcery over them, protecting the small group from the seithr and radiation in the air, allowing them them access to the facility. Both Nine and Trinity noticed that the area had seen small repairs since the arrival of the Black Beast. Deeper in the facility, the group discovered an elevator and entered it - after a brief while, its wires snapped; Trinity and Nine had made it to safety, but Ragna fell deep into the facility after saving Celica from the abyss. The three women rushed down the stairs to find Ragna, only to be met by a man clad in silver armor. After a brief exchange with Nine, he left; Trinity openly expressed her intuition that they would meet him again. With some further exploration. They soon found Ragna, who told them the knight's name - Hakumen Trinity found some odd bedrock away from the nearby cauldron, seeing behind it was a door to a hidden room - Nine and Ragna soon knocked down the entrance, discovering a hidden section of the lab.
Inside the lab, Trinity created light with her sorcery and dispelled her protective barrier since the cauldron nearby nullified the radiation. High above them rested the Kushinada's Lynchpin. Trinity fiddled with a computer, finding that the time in the facility had been distorted; the date was 2101, not 2106. She watched as Shuichiro Ayatsuki, Nine and Celica's father, appeared from nowhere and died in front of his daughters after explaining the Lynchpin. Trinity read and observed his numerous research notes, discovering that Shuichiro's research originally began when a man named Relius Clover came to him with a request. Seeing Nine's temper flare as she stared at the Lynchpin which could end the war at the cost of Celica's life, Trinity prepared a protective spell in case her friend's rage caused collateral damage.
The bolt sent from Nine towards the Lynchpin was deflected by a beastkin - Mitsuyoshi, who had met Celica and Ragna earlier on their travels. Trinity watched Nine fight against him; he wanted to use the Lynchpin while she wanted to destroy it. Their battle was ended by Celica, and Trinity helped strengthen the girl's plea for them to stop. She brewed tea for everyone to help diffuse the tense situation and listened to Celica deliver a speech on why she was willing to sacrifice herself to Kushinada's Lynchpin if it meant saving the world. Trinity hugged Nine, knowing how difficult it was for her to hear the speech, and listened as Ragna offered a different solution to the problem at hand.
Trinity brewed new tea, but Ragna refused it and left under the pretext of gathering his thoughts. Trinity was extremely surprised when she saw a sorcery circle light up in front of her and as a dark mist of seithr leaked from it. The group, consisting of Trinity, Celica, Nine, Ragna, and Mitsuyoshi, saw the Black Beast itself begin to arise from the circle. Trinity quickly stepped into a teleportation cirlce created by Nine and, together with Celica, left Ragna and Mitsuyoshi behind at their insistence. The three women were later in the Alucard Castle awaiting the return of the two men they had to leave behind. Here, Trinity became acquainted with Rachel Alucard and Valkenhayn R. Hellsing, having also learned that the previous head, Clavis Alucard, had recently passed away. Only Mitsuyoshi returned, as Ragna had allowed himself to be swallowed by the Beast, stalling it, and giving humanity around a year of time to prepare for its advance.
In the months following the events in the First District, Trinity joined a group of six warriors that were dedicated to the eradication of the Black Beast. Her fellow warriors included Nine, Mitsuyoshi (who had changed his name to Jubei), Hakumen, Valkenhayn, and a man called Yuuki Terumi; Trinity was later told that Terumi was possessing the body that she once knew as Kazuma, and grew attached to him because of the resemblance. Nine created a cane for Trinity that could transform depending on the sorcery applied to it. These warriors would later be known to history as the Six Heroes.
In the August of 2107, Trinity led a meeting in the Mage's Guild with the other Heroes. She made them aware of the situation between the representatives of each country who had been accepted into Ishana. The conversation quickly turned to the viability of Ars Magus, an Art developed by Nine. Trinity was curious about the nature of a Grimoire and was told that they were not always in the shapes of books. Their meeting ended when Nine realised that Hakumen had already left. The Heroes left to find their leader, seeing him with Celica. Trinity could not help but smile when she saw the affection between the two sisters, and left with Jubei for a nearby cafe while Seven and Eight demanded an audience with Nine and Celica.
Both Jubei and Trinity waited for Celica and Nine in the sister's favourite cafe. She ordered a milky tea and cheesecake as she waited; when the sister's came, Trinity watched Nine flirt with Jubei, bursting out in laughter with Celica over the exchange between the lovers. The atmosphere was disrupted by Terumi, who arrived and sat down to Trinity; she nearly called him Kazuma but caught herself mid-sentence. Celica caught a pained look on the girl's face as she made the mistake. Terumi went to the other side of the cafe and Celica attempted to cheer the group up once more, but accidentally pulled on Jubei's tails, making him flip the table which sent Nine's thick coffee all over Trinity's face. She let the group know her wrath as her glasses were dirtied. The two sisters began apologizing as much as they possibly could, although Jubei was confused over the fuss - he soon learned why Celica and Nine feared Trinity's anger.
The lecture began on forgiveness before shifting onto why people get angry, and then finally onto her personal opinion on why people get sad. They all left the cafe, and Trinity helped Terumi from his feet after he was viciously kicked by Nine for an inappropriate comment. She later left to work hard on the preparations for an attack on the Black Beast.
Another meeting concerning the Black Beast happened. Trinity's face was uncharacteristically dark throughout the meeting as she listened to Nine's explanation of the Beast's pattern of appearance. They agreed that they would need to deploy as quickly as possible to Eastern Europe and gather nearby country's armies to help in the battle ahead. Trinity watched as Rachel appeared to tell Nine that she could not personally help them, but gave them a hint telling them that the Beast would appear wherever Celica was.
Trinity had prepared alchemy based weapons for the unit that Jubei was to command in the battle against the Beast. When the time finally came, Trinity stayed with the main Ars Magus unit, using sorcery to communicate with everyone and command them across the battlefield. She reassured Nine that Celica would be fine as long as the Deus Machina: Nirvana and Hakumen were there to protect her from the Beast. When the monster finally appeared, she fell to her knees, fear having completely gripped her - the Beast was far larger than it was the year before. She watched as Seven and Eight summoned the Gigant: Take-Mikazuchi to Celica's location and forced it to take her power. Nine teleported next to Trinity and the two exchanged information on what was happening, with Trinity directing Nine's attention to Take-Mikazuchi. The weapon forced the Beast to retreat and both Trinity and Nine ran to Celica as fast they could, finding her unconscious.
Jubei had organized to take a Prime Field device for Trinity to inhabit, planning to steal it from the NOL. The plot did not go as planned, and the device activated its backup personality after having been attacked by a Fuzzy. Trinity watched as Rachel teleported a group consisting of Bell, Mai Natsume, Taro Sasaga'e, Shiori Kirihito, and Kajun Faycott to the 11th Hierarchical City of Shinatsu. She asked Jubei and Rachel to allow her to monitor the situation with Bell since it is her responsibility. 
Near the cauldron of the same Hierarchical City, Trinity interacted with Bell, being able to intervene thanks to her being so close to the cauldron itself. They talked, and Bell allowed Trinity to take over the body on the condition that she would be put into the Gallia Sphyras: Outseal. Now with a body, Trinity summoned Muchourin to her side, using it to help fight alongside Mai and Jin Kisaragi against the army of Fuzzy and Meifang Lapislazuli.  As the fight when on, Mai was captured by the Meifang despite Trinity's warning. Eventually, Meifang was defeated by Mai, and Trinity escaped the premise, eventually meeting with Jubei. The two talked about the fairness of the situation, and she revealed to him that Bell will always be by Mai's side inside of the Outseal. Trinity began to cry over what she had done, saying that the next time she sees Mai, it would likely not be in the body she had just acquired. 
Trinity lay inside Platinum's body as both she and Bang travelled to the Ikaruga Region. There was a point where she sensed the use of sorcery not far in the distance; what she sensed was Nine, bound to Izanami and forced to become Phantom, who had used Gravity Seed to immobilise Rachel and restrict Ragna under the Imperator's orders. She also told Bang about the Kushinada's Lynchpin, although details on it were scarce since her memories had been tampered with.
Trinity later found Hazama near the top of the Monolith in the 5th Hierarchical City of Ibukido. She attacked him, landing a mortal blow just below his left clavicle. This wound stopped Terumi's mobility and Hakumen landed Time Killer on the God, killing him, or so they had thought. Trinity, however, was stabbed by Hazama and dragged her off the Monolith. They fell into a nearby lake, both presumed deceased.
Platinum was later taken by Valkenhayn, who wished to speak with Trinity. Trinity saw this coming and attempted to run away, but regardless still ended up in the Alucard Castle. Thanks to Rachel's spells, she took over from Luna and Sena, and talked to both Valkenhayn and Rachel; the three had tea together as they discussed the plan for defeating Terumi. Eventually, Hakumen, Jubei, and even a resurrected Celica were taken into the Alucard Castle. Trinity fell to her knees and cried when she saw Celica, eventually hugging her and apologizing for everything she had done, feeling nothing but anguish and regret for what happened to Nine. Celica forgave her and the group formulated a plan on how to defeat and kill Terumi once and for all.
Trinity materialized Terumi's soul by using the Sekkigan, Jubei's fake eye. She then entered Terumi's mind and created several opponents for him to face, one after another until she battled him herself. Rachel and Valkenhayn pulled her out of his mind after he was materialized in the real world. The vampire teleported them to Yabiko and both Trinity and Hakumen were caught in one of Phantom's spells where they battled against a powerful shadow of Hazama, created by Phantom's pure hatred of the man. They defeated the copy and broke the spell that trapped them, revealing Phantom alone in front of an NOL building. Trinity and Hakumen's combined efforts revealed Phantom's true form – Nine, but she was covered in an aura that screamed murderous intent.
Trinity left Platinum, and found her way to the Arcus Diabolus: Bolverk, transferring her soul to the weapon. She eventually switched into the Mucro Algesco: Yukianesa, and formerly met Jin. They talked and she made a pact with him, using alchemy in order to make his body durable enough to fight – the only catch being that his body would eventually become completely unable to fight after an unspecified amount of time, but Jin still agreed to the terms. She was absorbed into the Embryo, but her memories were seemingly unaffected as she stayed by Jin's side inside Yukianesa.  Trinity became one of the chosen.
Eventually, she and Jin were transported to Ikaruga by Nine, who had told them both to kill Izanami to claim their piece of the Azure. She suggested finding Kokonoe, who could help them both in achieving their goals.  Eventually, they found Platinum, whose existence had nearly disappeared. Thanks to Jin's Power of Order, both Luna and Sena's existences were perceived, if only for a while – Trinity herself was given a materialised body by Platinum, and she properly met them for the first time.  The three of them later broke into a Sector Seven facility and retrieved data pertaining to Platinum's body before escaping.  She offered to adjust the body for Platinum, although doing so would mean that she would never be able to inhabit it again. Carl Clover found them, and offered to assist her so he could gain experience. 
Platinum was now fully recovered and trio parted ways with Carl. They were by found Jubei and travelled with him to Yabiko after hearing of Nine's hidden eleventh Nox Nyctores.  Before they did so, however, they dropped Platinum off at the Kaka Village so she could be safe from harm, and gave her the task to materialise Hihiirokane before leaving her to her task.  At Yabiko, she offered her expertise in alchemy to create a key that could be used to enter Nine's workshop. 
Trinity went as part of the strike squadron sent into Nine's workshop. Inside, Trinity listened to Nine's explanation of the world, the Prime Field War, her desire, and why she created the Corpus Sepulcro: Requiem. Ragna defeated Nine,  and she, alongside the others, were assaulted by Izanami and Nu-13 but thanks to Nine's use of the Radiance of Extinguishment to activate Requiem, they escaped but not before Trinity watched her best friend finally die. 
Celica's sorcery forced Rachel to teleport everyone out of the area to Celica A. Mercury's Church where Trinity chose to stay largely within Yukianesa without talking. She watched Celica die before she teleported back to Yabiko.  Trinity watched Kagura and Jin battle Azrael and win, and then as the world entered the final stages of Doomsday, begging Jin to hurry and find the others. She watched as Susano'o was reborn in the world  and when Hazama threw himself into the Boundary, his last words in the world remarking how much he hates her eyes. 
In the exterior of the Embryo, Trinity helped Ragna and Jin defeat Susano'o, putting Jin inside the Unit after Ragna dragged Terumi out of it.  She soon materialized clothes for Noel and took Jin out of the Susano'o Unit against his wishes.  Trinity told Ragna that taking her dream would be impossible since it had already been realized, and she threw the Unit deep into the deepest part of the Boundary, thanking Hakumen for all he had done for her. Trinity's spirit then finally passed onto the next life. 
- BlazBlue: Phase Shift 1, Chapter 1 - Island of Green Wisdom
- BlazBlue: Phase Shift 1, Chapter 2 - Cat of Crimson Sunset
- BlazBlue: Phase Shift 1, Chapter 3 - Mind of Azure Deviation
- BlazBlue: Phase Shift 1, Chapter 4 - Doubt of Yellow Equilibrium
- BlazBlue: Phase Shift 1, Chapter 5 - Night of Black Betrayal
- BlazBlue: Phase Shift 1, Chapter 6 - Voice of Emerald Evil
- BlazBlue: Phase 0, Chapter 4 - Chance-met Silver
- BlazBlue: Phase 0, Chapter 5 - Sealed Green
- BlazBlue: Phase 0, Chapter 6 - Promised Azure
- BlazBlue: Phase Shift 2, Chapter 1 - White Blade, A Flower
- BlazBlue: Phase Shift 2, Chapter 2 - Purple Ones, Their Theory
- BlazBlue: Phase Shift 2, Chapter 3 - Scarlet Guardian, the Doll
- BlazBlue: Phase Shift 2, Chapter 4 - Indigo Heart, the Conception
- BlazBlue: Phase Shift 2, Chapter 5 - Black Beast, Reappears
- BlazBlue: Variable Heart, Chapter 11
- BlazBlue: Variable Heart, Chapter 17
- BlazBlue: Variable Heart, Chapter 18
- BlazBlue: Chrono Phantasma, Story Mode, Chrono Phantasma, Episode 1: Unexpected Encounters
- BlazBlue: Chrono Phantasma, Story Mode, Chrono Phantasma, Episode 05: The Guided
- BlazBlue: Chrono Phantasma, Story Mode, Episode 18: Beginning of the End
- BlazBlue: Chrono Phantasma, Story Mode, Six Heroes, Episode 2: Year: 2200
- BlazBlue: Chrono Phantasma, Story Mode, Six Heroes, Episode 7: Destined Rendezvous
- BlazBlue: Chrono Phantasma, Story Mode, Six Heroes, Episode 8: Bonds of Fate
- BlazBlue: Central Fiction, Story Mode, Episode 001, Chapter 003
- BlazBlue: Central Fiction, Episode 005, Chapter 037
- BlazBlue: Central Fiction, Story Mode, Episode 009, Chapter 064, Sub Scenario 1
- BlazBlue: Central Fiction, Story Mode, Episode 009, Chapter 073, Sub Scenario 1
- BlazBlue: Central Fiction, Story Mode, Episode 009, Chapter 073, Sub Scenario 2
- BlazBlue: Central Fiction, Story Mode, Episode 010, Chapter 077, Sub Scenario 1
- BlazBlue: Central Fiction, Story Mode, Episode 010, Chapter 078, Sub Scenario 1
- BlazBlue: Central Fiction, Story Mode, Episode 010, Chapter 079
- BlazBlue: Central Fiction, Story Mode, Episode 010, Chapter 081
- BlazBlue: Central Fiction, Story Mode, Episode 010, Chapter 082
- BlazBlue: Central Fiction, Story Mode, Episode 010, Chapter 087
- BlazBlue: Central Fiction, Story Mode, Episode 011, Chapter 092
- BlazBlue: Central Fiction, Story Mode, Episode 011, Chapter 094
- BlazBlue: Central Fiction, Story Mode, Episode 012, Chapter 096
- BlazBlue: Central Fiction, Story Mode, Episode 012, Chapter 097
- BlazBlue: Central Fiction, Story Mode, Episode 012, Chapter 098