Aizen the big cheese of Bleach. He can’t handle Bass. Many will disagree with a passion but I think Bass can win without thinking about it much. Aizen did just get a super form but Bass will just take his power. Bass wins.
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Not if Aizen traps him in an illusion first.
I’m not sure how well an illusion would work on a being made of data. Still, it’s been shown that you can break illusions with raw power If Bass had too, he could just level the planet and be done with it