The earliest information known about Grimwood is that he saved Karenjina Parsett from a laboratory that forced people to awaken their own Drives, and she would later serve under him as part of his squadron in the NOL.
Ikaruga Civil War
Towards the end of the Ikaruga Civil War, the Ninth Squadron was placed on the front lines. Here, they received a new member - Jin Kisaragi, and the squadron were immediately deployed as part of an emergency deployment. Their mission was to recover a Nox Nyctores that Sector Seven had stolen, but they had arrived at the laboratory two hours late, and were attacked by the corpses inside the facility. After disposing of the necromancer (revealed to be a doll under Relius Clover’s control) that was moving the corpses, the squadron left the facility.
Grimwood would later tell Jin that Tenjo Amanohokosaka is the Imperator of the NOL, and that he had a plan to prematurely end the war by finding the object that he believes the war revolves around, and then destroy it (the object in question being Kushinada’s Lynchpin). Thanks to Karenjina, the Ninth Squadron discovered the hidden entrance to Kushinada’s Lynchpin, and Grimwood ordered that Karenjina and Corporal Honoka stay behind. The unit discovered ancient writings, and Grimwood believed the enemy they are searching for to be responsible for distributing weapons to the NOL, Sector Seven, and Ikaruga. After being urged to go deeper into the facility by Jin, the squadron were separated from the former.
Inside the area, the Ninth Squadron were ambushed by Meifang Lapislazuli and the Wings of Justice division of the NOL. Three of the squadron’s members were killed, and Grimwood lost to Meifang’s overwhelming strength. She publicly denounced him as an ally to Kokonoe, and he, in turn, called her a monster. Outraged, Meifang effortlessly decapitated him.
Grimwood’s death would deeply distress Karenjina, and serve as a motivation for Jin to prematurely end the war. In its aftermath, Jin was ordered by Kagura Mutsuki to pursue Meifang. Alongside Mai Natsume, Jin defeated her, finally avenging the Ninth Squadron. While fighting her, he remembered the ordeals that they had faced together, and the Grimwood's death. 
- BlazBlue: Variable Heart, Chapter 18