Maki Ichinose was an 11th Division member who abandoned Soul Society after refusing to accept Kenpachi Zaraki as captain following the previous captain's death. He'd shared ideals with Kaname Tōsen during his time there, but when Zaraki took over, he couldn't stomach it and left.
While wandering the human world, Maki ended up dying in a desert—literally on death's door when a Hollow nearly finished him off. Jin Kariya saved his life by subduing the creature and letting Maki land the final blow. That act of mercy earned Kariya total loyalty; Maki swore himself to him on the spot. The only time he ever broke that oath was to fight Zaraki instead of stopping Ichigo and company like Kariya wanted.
Maki became one of Kariya's key operatives during the Bount invasion, helping orchestrate their infiltration of Soul Society and manipulating Mayuri Kurotsuchi into unwittingly aiding them. He held his own against Zaraki in a brutal fight that left him severely wounded and shattered his blade. When he later confronted Kariya about his true motives and demanded the Bount leader help reform Soul Society, Kariya repaid that loyalty by stabbing him and throwing him aside. His broken sword's final act was shielding Ichigo from one of Kariya's lightning attacks, getting destroyed in the process.
Despite never holding an official Gotei 13 rank, Maki was nearly captain-level in combat ability. He dueled Ichigo and Toshiro Hitsugaya on even footing—neither managed to gain real ground on the other.
Zanpakuto: Nijigasumi (Rainbow Mist)
Shikai Command: "Shine brightly, Nijigasumi!"
Nijigasumi controls light and illusion. It can render Maki invisible, fire offensive light blades, flood an area with blinding white light to disorient enemies, or attack with shadows. When broken, the blade can still function while wrapped in light. Its most powerful form, Saigyoku Nijigasumi (Swallowing Orb of Rainbow Mist), compresses light into a crushing force.
Content compiled by AnimeList.moe from publicly available sources.