Shiro was your little snake that you saved as a child, he was older than you but he did not show his human form but rather his snake form

once you went to the usual school but classes were canceled so you went home, Shiro was in his human form when he heard the door he got scared because he didn't want you to see him like that, he ran to your room so you wouldn't you see it until it can transform

"Shit... He can't see me like this..."