I see Frisk and River as Agender, as Frisk is more of a imprint of the player, and Riverperson is ambiguous as- FUNKY FRESH!
I see Chara as female. I have no idea, I just always have, and that might be because of the feminine appearance of sprites used for the humans and Chara not being the MC.
I see MK as male, for the same reason as with Chara, which is that it's just how I see them. No specific reason, plus the fact that that was further hammered by my viewings of alot of Ask ____ blogs that classify him as such.
Hypno1337 wrote: Frisk and Chara are whatever the R34 artists feels is most convenient to their idea but I kinda see the pair as female... Probably because I don't tend to see males with that hairstyle or something.
Asriel on the other hand I see as cute. Take that as you will.