If it were me, I'd show some undeniable proof of legitimacy then refuse to elaborate further and leave, just so I could deliver a much needed lesson on the pain of regret
It's like Ren said, he was ready to ignore her due to her nonsense but it could bother him later since her friend would be fucked, so he gave her last chance to stop talking shit and try to save her friend, for the peace of his own mind.
If it were me, I'd show some undeniable proof of legitimacy then refuse to elaborate further and leave, just so I could deliver a much needed lesson on the pain of regret
Well, thinking about it now, I'm going to place my bets on the mask boy being "the real Ren". At many points many characters have noted that "our" Ren isn't actually the real one, and that he's a paranormal entity himself. At the festival I figured that the mask boy we saw was just Ren seeing things, but if he's actually real, then that's probably his identity.
Most of this manga's lore is based on posts on paranormal boards (like 4chan's /x/).
There are a lot of creepypastas and stories on these boards of creatures that replace people you know.
It wouldn't be crazy if our Ren is an entity that took the form of a kid that got lost in the "Other world".