All of it. Anything backstory like is canon. Basically, think of it movies this way. Every character, at the point of development in the manga, past intact, were transported to an alternate world for a day and then transported back. Honestly, if you guys read comics, you would not be stressing. In one collection, the same book, part of the same storyline, I had to stop this "oh but if so and so was this then why is such and such that" because otherwise, it's a stroke I'm collecting.
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Shocking, but somehow not. Are Door dude and Soap lady CP0 agents?