I don't like the fanon/headcanon that helia should be a fairy. They don't headcanon this with the other boys but only with helia because helia is the pretty long-haired pacifist boy who can use magic. (He doesn't use it like nabu, but he can use it.)
I've only seen 1x someone headcanon riven as a fairy and made pretty fairy fan art of him, and "fans" were dogging on the artist for drawing riven like that. So yeah.. fans who headcanon helia as a fairy, they do that because he's a pretty boy who looks like a girl.
(I actually know what you are talking about. I can't remember the artist but they made fan art of Riven as a fairy. It was pretty art too. Not a joke/gag thing. But ''fans'' were calling it gross.. only because it's Riven. The artist eventually deleted it because said ''fans'' didn't know how to not be an ass. )