I used to prefer using the term Sensei, but then I saw Selebus using the name 'Akira' instead of 'Sensei' when posting here. Since he did so while in a position of presumable safety and comfort, I imagine that in his mind he uses 'Akira' too, and that would make it the more 'canonical' name, or maybe there is some other purpose there, but either way due to that I slant towards Akira as well. It may be that the name 'sensei' is associated with evading responsibility (like: "It wasn't me, it was [generic protagonist title]") and so he used Akira here to reject that disassociation and lay blame flatly at his feet.
I'd go further, taking his title as his only name was essentially denying his own personhood so he didn't have to feel anything. Primarily guilt for his actions, but also grief, and basically any emotion other than lust. I think its useful when discussing his character to acknowledge him as a person, even when he does awful, awful things. Especially when he does awful, awful things.
First: How is that characters name a "major spoiler"? He could be named "Biggus Diggus" and it would change (afaik, and i might be wrong, but doubt it) absolutely nothing. It's not like Akira is the keyword to "solve the game", if it actually can be solved one day.
Devil's advocate: at the beginning of the game Sensei and Maya operate under the pretense that Sensei is some nameless ghost thing that got isekai'd into Akira's body. The name in particular might mean nothing to a new player, but that it refers to the MC could tip them off early that that idea is incorrect.
But again, that was years ago. There really isn't any discussion we could have about Sensei/Akira that wouldn't spoil that. And really, the entire plot of the game is a spoiler. The whole time loop thing, as well as all the supernatural god stuff, are sort of early game reveals. So basically all discussion of the game would have to be spoiler tagged, which to me would be the same as none of it being spoiler tagged.
So yeah, the most we should be doing is not openly posting "gosh I can't believe Rin was an alien this whole time!" 10 minutes after an update comes out. And maybe using spoiler tags when direct replying to a new reader.
If it turns out Rin is an alien today I am so sorry