Guessing the boy who "made her smile" as a kid is probably the mc and neither of them realize it, or she knows it's him and was trying to talk to him from before the first chapter...
@lololol lololol i think youre right, even in chapter 1 she was shooting him glances and looking back i think she was trying to work up the courage, and that also might be why she called rin-kun when she passed out.