Hello anon! Sorry for the late response.
I don’t know how good I am at giving advice but I’ll try.
I’m Korean, so it’s harder to give advice that makes sense or helps (I write a lot from my own experiences) but when I make my headcanons I try to subvert a lot of stereotypes . Basically what I do is:

See character I like
Immediately say they’re Korean with no hesitation
For example, I rarely see people headcanon the Mooninites from ATHF as Asian even if it works really well because most can’t imagine rude and brash characters as Asian.

Everything else falls into place pretty much after and I like to associate canon traits as “evidence” as them being Asian .
(Ignignokt’s eyes for example , and the fact the Mooninites frequently talk about Los Angeles, a place historically connected to Koreans and Korean-Americans.)

Everything can be Asian if you try hard enough .
As long as you don’t fall into:
- Only making your Asian head canons with “softer” or more effeminate characters among other stereotypical traits (Math nerd, strict parents, cold and apathetic etc)
This doesn’t apply if you’re making everyone Asian like I tend to do.

• Mix cultures incorrectly / get their culture wrong
• Not making them being Asian their whole personality. Or whatever. This part I don’t really care as much about as long as you’re respectful about it

In the end, I started my koreaposting years ago because I rarely saw people talk about Korean headcanons in fandoms (even if there are other Asian headcanons , Korean ones were pretty scarce) so it basically became my mission to spread propaganda . All I can really say is do your research into the culture, especially if you are doing characters more connected to their mainland and not Asian-American.

My “headcanons” more often than not aren’t really headcanons but an assertion of fact or a “theory” so I often also read websites like TV Tropes to see what Asian tropes the character fits into and work from there.

If you need any clarification I’m happy to elaborate because I really am not the best at advice and I’m usure if this makes sense. Thank you for your question!