Fan Casting Resentful Outnumbered Sibling in Sort by Tropes

Being the only son or daughter in a family with three or more children often comes with some resentment and loneliness. The other siblings are presented as a pair or group that the outnumbered sibling can't relate to, leading to them feeling left out. The resentment is often played along gender roles, where it's portrayed as difficult for a guy to relate to dolls and tea parties, or for a girl to relate to sports and toy cars. If not, it might be around the quirks of growing up with male and female bodies, for example, a guy is disgusted by his sisters talking about periods around him.