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Thoughts about Akechi because he's infected my brain
We really never see the "real akechi" in Persona 5 or even in Royal, I think. That's not to say there aren't honest moments and real emotions, but every moment we have with Akechi is him trying to get us to serve some greater goal of his. In vanilla that goal is obvious: he wants to get close to you to further his vengeance on Masayoshi Shido. In the third semester that goal is less obvious but I'd say he wants you to think he's an irredeemable monster and that you shouldn't care about him so you reject Maruki's deal. Third semester is slightly more honest with Akechi- his convictions and feelings are all real, but he portrays them in whatever way will get you to do what he wants while keeping you at an arm's distance.
I think the only moment in the whole game where Akechi isn't putting up some sort of mask is after you beat him in the engine room. Before he's kinda having a big feelings moment so while it's honest, it's an extreme. After? He has no more reason to act, he just has his one request: destroy Masayoshi Shido in his stead. And you do, for the last request of the boy you never really got to know.
So who is the real Akechi? I don't think Akechi knows himself, I think he's lived so many years with a mask as Shido's Assassin or the Detective Prince or a pleasant boy that he doesn't know which is real. I don't think we'll ever see the real Akechi, not in anything mainline, both because they better not be making another Persona 5 and because there is no 'real' Akechi without the masks, without the deception. His character is like Joker's, he's constantly tailoring himself to be what he needs to be because that's the only way a bastard child like himself can survive. It's why I like wildcard Akechi fics so much, because he's just as malleable as Joker. They're rivals, after all.