Here are some characters from who I think, they're asexual.

Gamora (Marvel)

aro-ace

The Brave (Pixar)

aro-ace

"I am Merida and I'll be shooting for my own hand!"

Todd Chavez (Bojack Horseman)

ace
canon

Spongebob (from Spongebob *surprise)

ace-homoromantic

Sherlock Holmes

ace, maybe greyromantic?

"You don't have a girflfriend?"
Sherlock: "A girlfriend, no, not really my area."
"All right. Do you have a boyfriend? Which is fine by the way."
Sherlock: "I know it's fine."
"So you got a boyfriend."
Sherlock: "No."

Saiki K (from an anime: Saiki K)

ace

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Disclaimer: This is only my opinion <3

Do you know any other headcanon or canon ace characters?
I'd love to add them to the list :)