I'll say it again, I don't get it, this drama.
Jun, Reiha, just the "of youth", ok.
But what Mizuo believes he did wrong that he regrets? Why any of this is his fault? Please, explain.
I think Jun's an actual idiot and Reiha is annoying and resented. Mizuo needs to let go of the past and realize these people aren't good friends anymore.