>>32453347A scenario presented by an artist I follow. Sun actually dressed as and pretended to be a female, Chicken-chan, until quite some time. Lillie began to see "her" as a true friend, as "she" was a girl Lillie's age. Once Lillie changes her outfit and resolves to try even harder, Sun is impressed and follows her lead. He too stops crossdressing, surprising everyone that "Chicken-chan" was actually a boy.
Pure autism. I like this autism. Pic related is when he reveals it to Lillie and her first reaction.