One. I know of one canon asexual character. Lucky for us, she’s a goody. Voodoo, from the show Sirens. She’s tiny and cute and friendly until you annoy her, and she has incredibly morbid interests.
They have a whole episode looking at her asexuality in season one.
One of the dudes gets a crush on her, and the other guys as well as Voodoo herself basically tell him to give up now, because sex is not on the table.
Instead of losing interest, the guy does a bunch of research
And he decides he wants to be with her anyway
Seriously I can’t tell you how happy I was watching this there were probably tears
And while I’m here and harping on about Sirens, one of the main characters is a gay poc
And the show itself is really funny and unique.
So in summary, Sirens is awesome and Voodoo kicks ass.