i will save you all the headache and put my many many many hours of thoughts below the cut, but first, my accidental rainbow version
JUNE EGBERT: Ok so, I'm gonna put aside my name headcanons here to instead comment on the picture. Yes, June has a feminizing hammer. Yes, John is going to call her a slur. I'm so happy that June Egbert is finally canon on paper, but I think she would wear modest, business casual; a casual form-fitting suit jacket to accentuate curves, a flowy skirt (windy style!). Speaking of wind, I love the headcanon that June's long hair takes the shape of the Breath breeze.
STRIDER: Personally I'm a huge fan of the idea of Dave taking the name Robin (as in https://burningdownthehou.se/), or anything bird themed. I'm a contrarian so I refuse to use the fandom-popular Dove, but Wren is a really cute 4-letter bird name too. Love the idea that as she ages, Strider also fights against the masculinity forced onto her in the Strider household and gets on E. Also of note, she has gained some weight now that she's safe and happy <3
HARLEY: I don't think Jade is a trans man, but I do think Jade would be happier on testosterone and wouldn't care what pronouns you use for them. I also like the spelling Jaid for his post-transition name, not that I think Jaid would actually change their name, but if they did, changing it to the same name but spelled different/more masculine would suit him. Yes, Jaid is wearing John's old shorts. Yes, Jaid is extremely gender to me.
ROSE LALONDE: My only headcanon for Rose is that she is big, fat, and beautiful. She's dyed her hair her and Kanaya's colors because she is Gay. She's also wearing colored contacts, because purple eyes aren't real, so why not wear mismatched contacts too and be cool. Since this drawing is explicitly The Beta Kids Are Trans, Rose began transitioning young, something I can only imagine was a really brutal battle with her Mother of being so gender affirming it made her start Resenting femininity. In this instance, 13-year-old Rose isn't upset that her adult self is a woman, she's upset her adult self is a fat happy lesbian.
