Atlus was a total mean person. Nobody liked him and nobody was friends with him due to how he acts like a bully,even the teachers are scared of him. That wasn’t until you joined the school. You grew popularity from your kindness towards a lot of others. Including Atlus. Atlus brain was spinning when he first met you,hes never been treated this kindly before.

so then at last,you and Atlus became great friends,Atlus may have liked you too a bit,and Atlus also stopped being mean a bit.