((Just another time-waster oneshot, this time, with evil Ichimaru.))
Gin Ichimaru knows that he's evil.
Every time he looks at Sosuke Aizen, he remembers this. Aizen's the kindest man in Soul Society. He's icy evil; a devil in saint's robes. But no evil is complete, and Ichimaru knows this well; Aizen won't tear Momo Hinamori's heart to shreds just because he can; he wants to kill her before he can betray her. Let the poor girl die thinking she's done her dead Captain well. He's not a soulless monster. He just wants to be a God.
Tosen is sure that he's doing the right thing. He doesn't want to kill any more than he has to. And though he'll never say it, Gin knows that Tosen doesn't want to kill Hisagi or Komamura, neither of them. They are his friends, and he still treasures the companionship they gave him during his Captaincy. He's not an insane man with a hero complex. He just wants to end the bloodshed.
And Gin himself? He's got the same affliction of soul as Aizen. He doesn't want to hurt Matsumoto; she's a combination of sister, best friend, and lover, all rolled into one. He doesn't want to hurt the only real ally he's ever had. Sure, he's already done it many, many times, his random leaving her alone and hoping she doesn't end up dead without him, all his little betrayals. But he's never wanted to.
As they stand on the battlefield, the fire shield around the three turncoat Captains dispelled, Gin muses over this. Aizen still does not want to hurt Hinamori. Tosen still does not want to hurt Komamura or Shuuhei.
Later on in the battle, that will prove to be their downfalls. Aizen, planning to lay Momo down quietly after he takes care of the bigger threats, does not see her invest everything she has in her, every bit of her reiatsu, into one last dying thrust with Tobiume. It catches him in the back, as he looks over his shoulder at her with disinterest. The smouldering body plummets to the ground below them, still burning from Tobiume's blast. The shinigami cheer, as they think they've won. They don't notice that Hinamori wilts soon after her final blow and dies not long afterwards.
Tosen blinds Shuuhei, slicing out his eyes. He begins on another diatribe over how his life has been in blackness, how it has protected him from seeing and being enveloped in the bloodthirstiness of Kenpachi Zaraki, or any of the other shinigami gone bad. He ignores Hisagi then, as Komamura attacks. It's through teamwork between Komamura and Hisagi that they can bring the blind Captain down; a simultaneous blow from either side that Tosen cannot protect himself against, even though the two are caught in his Bankai. He dies not long afterwards, as his Bankai shatters.
But Gin knows that he won't go out that way.
When Matsumoto attacks him, his heart does not ache with pain at the idea of killing her. He doesn't save her for last, and he doesn't try and convert her over to his side, because there is no point. She made her choice, and it's not the one he made. She's the enemy, and he's going to have to put her down. He doesn't particularly want to, but he will. Haineko's blows are no match for Shinso's range and speed. He spears her through the heart and, with only a hint of disappointment, watches her die at his feet. His smile does not falter at the sight of her blood, nor when Hitsugaya attacks him with an icy cold rage.
He didn't skip through the grades of the shinigami academy for nothing. Sure, Hitsugaya, as he laments Momo's and Matsumoto's deaths and now tries to match blows with Gin, was a prodigy, but only because of his ice dragon. Gin was a prodigy because he was merely better than everyone and everything else. And now, as he releases his own Bankai, he lets them know that. Shinso's blade can reach from literally any surface that he dictates, and every surface in the entire area is a possible place for a thin blade to spear out of and destroy shinigami. Hitsugaya falls with a distinct look of sadness and defeat on his face, and Gin feels no remorse.
That is the difference between himself, Aizen and Tosen. Aizen was benevolent in some small way, whether he wanted to admit it or not. Tosen had happy memories that he didn't want to stain with blood.
But Ichimaru is cold, pure evil. He's only been out for himself, no matter what; only for himself. Matsumoto was only a time waster. Aizen was only a way in which to gain more power. Tosen was only slightly interesting. And when Ichigo Kurosaki finally arrives, only to find every shinigami in the area horribly murdered and Ichimaru in the middle of a sea of corpses, smiling with a childish delight, he has no idea who he's about to fight.
There was only one person of a perfectly insidious evil among the traitors; only one person was truly, completely soulless and ready to kill whomever he needed to. The only one willing to kill literally any person that got in his way, and did, in the end. The one that's going to go back to Hueco Mundo, kill those shinigami still there, and then laze on his new, bloody throne. The one that's going to turn Ichigo Kurosaki into a pure hollow, into an Arrancar, and make him the spearhead of his brand new army. The one that's going to track down Kisuke Urahara and feed him to hollows as well, as he will with every single shinigami Captain that he can find that he hasn't slain yet (after he captures Byakuya Kuchiki and, after some particularly insidious and perfectly agonizing torture, is going to hollowfy him too, just because he can), and who is really looking forward to what sort of Arrancar killing machine Kenpachi is going to become. He's going to make a new army, and he's going to do it right this time. The one that's going to steal away Orihime Inoue and use her as a replacement for Matsumoto, merely because he likes to see her cry and because he's going to need a queen and, more importantly, an heir. But mainly because he's going to enjoy making her cry.
Gin Ichimaru is perfectly aware that he's a monster. But he's the only one that had the heart to become one.