Baishin

Baishin is a middle-aged man with graying hair and a beard, marked by two red symbols on his brow and by blades that jut from his shoulders. He wears armor of a samurai cast layered over his Shinigami hakama.

Baishin comes across as a savage killer who cuts down everyone in his path, yet the frenzy stems from his inability to undo the merger with his own Zanpakutō. Desperate to be parted from the blade at any price, he hunts strong opponents to drain their spiritual energy, hoping to spark a blast fierce enough to split the two of them apart even if it destroys him. When Ichigo Kurosaki finally cleaves him in two, he dies content, since the strike accomplishes exactly that.

Four centuries before Ichigo Kurosaki inherited Rukia Kuchiki's powers, Baishin found the means to fuse himself with his Zanpakutō in pursuit of greater skill, only to find the change permanent. Driven into a rampage, he slew sixty-three seated officers, some of them lieutenants, before escaping to the living world; of the six captains dispatched to stop him, two were killed and the rest managed to bind him inside a statue.

Ages later Baishin breaks loose, killing all around him and stalking those with strong spiritual pressure. He corners Renji Abarai and Ichigo, shrugging off Renji's fire before draining part of Ichigo's power, and only retreats, scattering a wave of Hollows, when Tōshirō Hitsugaya arrives. Tracked to the ruins where he was once sealed, he faces Ichigo again, and by absorbing a large share of the youth's energy he unleashes a Bankai that turns his skin to metal and remakes him as a living mass of blades. Ichigo answers with his own Bankai and cuts him down, leaving behind only the sword he had fused with. As Yoruichi Shihōin surmises, Baishin had sought to use Ichigo's power to tear himself free of that blade at last, whatever the cost.