The Sankishin (三輝神), also known as the Original Units, are three units with unimaginable power over time. They are: the Amaterasu Unit, who governs time; the Tsukuyomi Unit, who protects time; and the Susano'o Unit, who slashes time.
The Sankishin were first discovered after Susano'o made himself known to humanity. Amaterasu was pivotal to the Prime Field War, taking The Origin as her first wielder. At the end of the war, The Origin created a new world using Amaterasu's power. Tsukuyomi was put into Rachel Alucard at some point, while Susano'o bounced between owners before primarily being owned by Hakumen. Little else is known about them other than they came from the Age of Origin and it is unknown how they were made or who made them. The Nox Nyctores were based on them, while the Lux Sanctus: Murakumo was specially designed as an 'Anti-Sankishin' weapon. The Sankishin are comparable to gods.
Amaterasu, also known as the Master Unit, governs time, and is arguably the most powerful of all the Sankishin. It has complete dominion over Phenomenon Intervention, being able to Observe anything and make it a reality. Its powers include rewinding time, turning an Embryo into a world, and general Phenomenon Intervention. It resides primarily within the Boundary, but can be coaxed into the world through the Nemesis Horizon. Amaterasu was responsible for the timeloop that plagued the world between 2100 - 2200.
Amaterasu can choose a humanoid as its Eye of the Azure, giving them immense Observational power. Its current wielder is The Origin, and its location is unknown. Amaterasu and Susano'o are locked in a constant cycle of creation and destruction.
The Master Unit takes the shape of a giant metallic object, similar to a satellite, that has multiple spires and banners flowing from its body.
Tsukuyomi protects time, although little information is known about it. It's strength lies in that it can block any attack with its impenetrable shield, being able to withstand multiple blows from Gigant: Take-Mikazuchi without any sign of breaking.
Tsukuyomi's current wielder is Rachel Alucard, who stores it within her own body when it is not in use. Its appearance is unknown.
Susano'o slashes time, and is the most unique of all Sankishin. It gained a soul through unknown methods, and grew to hate Amaterasu for being locked into the cycle of creation and destruction. Its soul separated itself from its body, becoming known as Yuuki Terumi, and went on to commit a slew of vile acts throughout his life.
Susano'o appears as a set of armor that encases the entire body - it normally appears as a set of white armor that is reminiscent of that wore by samurai. When used by its original owner, Terumi, it becomes dark green, growing claws, teeth, and appearing far more ferocious. The Susano'o Unit has an incredible amount of strength that it gifts its user in combat.
BlazBlue: Central Fiction Library Entry
The basis of all Phenomena Weapons, also known as the 'Original Units.' They are individually called the 'Amaterasu Unit', 'Susano'o Unit', and 'Tsukuyomi Unit', but details about them are unknown. The 'Amaterasu Unit' is also known as the 'Master Unit.'