kagikko
A key child is a fan of Key, the game company. They love their games so much they might throw a hissy fit if you say Clannad is the best.
My friend is a key child. He cried when Air ended and then spent a month trying to convince me it was the best game ever.
My brother is a key child. He plays Kanon every day and still thinks it’s the best game ever made.
I’m a key child. I once fought my cousin in the mall over who loved Clannad more.