help pls

okay so i read this manga (idk if it is a manga im just going to call it that) a while ago and can't remember much except for the ML like didn't know anything about the world and the FL had a little sibling who defended the ML saying something about how the kid forget's to brush their teeth in the mornings or at night sometimes but the ML brushes his after every meal or something like that
ik this is like nothing to go off of so like I'm not expecting anyone to know what I'm talking abt but I thought i'd be good to at least ask