hmm... you know, I guessed this 100 chapters ago, but now that I'm thinking about it, this would make more sense as a final confrontation deep within the bowels of the enemy lair, in a properly shounen style. A single gunshot in an old science lab just somehow doesn't seem quite fitting, and everything up till now has at least been fitting of a shounen story. If Friend is Fukubei, then that corpse is not Friend. And if Friend isn't Fukubei (the more likely option, now that I can consider how things ended up), then they pulled another Sadakiyo where they turned him into a pawn. God, if the final reveal is that it's Kenji, I'm gonna flip.