The girl have an illness

For most of the male protagonist's life, he hasn't had friends, pursued friendship, or entertained anyone who approached him. However, then comes Ayaka, bubbly and for some reason wanting to talk to the boy who goes out of his way to isolate himself. This comes as a shock to everyone and raises quite a few eyebrows. Yet, slowly but surely, due to her persistence, the male protagonist warms up to Ayaka and arguably falls for her.