Oh he is shisitoren(i dont remember the right spelling😭) mom hihi loved that but why da...

I think they added him because they released a game and in that game they touched more about Shishitoren's story and he appears there. If you remember, the special chapter with him shows that he cared deeply about the team, but he had a disagreement with Toji about the direction they were taking as a team. That plus personal problems (he had to take care of his younger siblings) made him leave Shishitoren for a while, but he came back now that things are better.

Wait there's a game!? Anyways got it thanks for clearing it up