Shūsuke
Amagai

Shūsuke Amagai took the 3rd Division captaincy after Gin Ichimaru's defection, arriving as a friendly, capable officer who bonded quickly with Ichigo Kurosaki and appeared to be exactly what the division needed. He is the antagonist of the anime's Kasumiōji arc and he engineered the whole thing.

His father was a Shinigami killed on Yamamoto's order, and Amagai has spent decades building a route to the Captain-Commander. He entered the Gotei 13 under a false name and a false Rukongai background, researched the Bakkōtō, earned the trust of the Kasumiōji clan, rose through the Patrol Corps, and took a captaincy, all of it aimed at one man.

The Bakkōtō is the flaw in the plan. It is a weapon that feeds on its wielder, and Gyōkaku Kumoi gave him his knowing that. What Amagai never lets himself examine is why his father was executed, and when Yamamoto finally tells him, the revenge collapses under him. He takes his own life having spent everything on a story he never checked. Raika, his Zanpakutō, is a fire sword with a lever on the hilt, and it is a genuinely inventive design wasted on a man with one idea.