Is Nagisa actually Akira-sensei's daughter? A shaven, younger Akira-sensei kinda looks like Nagisa's "forgotten" dad. I'd bet Erika pulled some strings to get her dad to have that one affair with his coworker. Somehow set up a honey trap with the help of money or something. Cheating is still bad though, so I don't feel sorry for him. If he loved his wife and daughter he wouldn't have cheated, unless someone was blackmailing him with his life or their lives on the line but I don't think that was the case.
On page 25, her name is Mari Banri, not Mari Mari.