Board Thread:General Discussion/@comment-4976518-20140808063123/@comment-10330822-20191026190822

So you think its, perhaps, similar to Tsukuyomi from Naruto? Where the strength of the illusion is so strong it can actually kill the person outright? Like through mental trauma?

I guess that's possible, the only problem is why wouldn't he just use it to kill off the Gotei 13 right away rather than engaging them. Likewise, as you said, Aizen needs to handle his enemies personally in Shikai, but if his Bankai circumvented that, why not just use it to kill Yamamoto with it rather than do the round about method of creating Wonderweiss.

To me, the fact the illusions aren't fatal is part of the reason Aizen needed to become so strong individually, because unlike normal Shinigami, Aizen can't rely on his Zanpakuto to finish fights. And in that way, it stops Kyoka Suigetsu from becoming overwhelmingly OP.

That would make more sense as to why Aizen needed a trick to deal with Yamamoto, as Yamamoto is the only Shinigami who actually rivals Aizen in overall ability. That, plus my theory, would make sense why he didn't use Kyoka Suigetsu to finish Yamamoto, because there was a chance it wouldn't have been as effective unless he got the power-up from the Bankai.