@Crossword:
Ishigami did the part where Luffy and Blackbeard clashed right? The eye distortion instantly stuck out to me.
Yes, that was my first assumption.
I need to watch it in better quality, that Akainu Vs Luffy, Zoro Vs. Fujitora, Sanji Vs. Kizaru were very familiar.
Ito, Mitsui, Nakatani have also worked on it.
–- Update From New Post Merge ---
My take on the Opening Animation:
???:
!
Yoichi Mitsui:
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Hiromi Ishigami:
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Takashi Hashimoto
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I think Shuichi Ito did the meteor falling, and probably most of the beginning part where Luffy, Usopp, and Chopper chase the beetle, but I'm not very sure.
Mr. Horisawa just told me that Mushi Productions were in charge of today's One Piece. Mr. Kitazaki is from Mushi Production. Mr. Horisawa was asked by Mushi Production to work on today's ep, he says that he often works with them. Actually he read my tweet where I said that Horisawa and Kitazaki might be friends since they work together in the same episodes, and he was trying to correct me.
BTW, Mr. Horisawa's scenes from #629, From where the first newspaper is falling to scenes of explosions in the battlefield. Also, Doflamingo walking to the room before the end of first half.
Edit: I asked Hashimoto, he said that he did the meteor falling. Just 2 cuts.