The dude's mother confessed earlier that he didn't socialize at all and had zero public skills. The sister knew how to help the FL with the notes becasue she had done the same for her brother. That's kind of my own speculation but have full confidence that he is our ML due to how often the auther has kept his character elevant as the story progressed. if anything, i'm astounded at how well the auther made it seem. No forced sudden character, we knew he exsisted but he was mentioned briefly and the auther didn't linger on the content involving him so She did a wonderful job in making his apppearance natural to the story line as well as suspensful for the readers. It all tied wonderfully together. like a cherry stem and an S+ Class kisser ;)
Alright guys, i see lots of confusion in the comments section so here is the clean version without any spoilers of whats going on. So we all know she somehow returned to the past after she was killed. During her return there was a cloaked figure shown that saved her after her death. They then hint about it during the entire manga. Her ettiquet I cant spell so please forgive me, teacher has two kids. The daughter who became her first friend and a son whose in the magic tower but rarely leaves. Throughout the hints many might have assumed that it was her father who turned back time because it was shown that it was a male with blond hair, however when the lady mentions her son, he is also similar to the man who saved her. I do believe this guy is the ML you have all been curious about because he has been mentioned several times thus far to build his entrance. So far he looks bad but his mother admits to him having ZERO social skills and so does his sister. so in all reality he is a male version of her.