Upon googling around, I found these characters -- yzak and rey -- in Gundam Seed Destiny, seemingly matching the artist's comment "イザークとレイ/izaaku and rei". This would also indicate that this painting has yaoi tendencies.
Can anyone confirm this?

Eh, no. I don't think Yzak and Rey ever exchanged a single word, or were ever in the same scene. They are both however normally the victims of yaoi fan pairings with other people.

...well, in Rey's case, maybe not entirely fan-made.

This is NOT crossdressing. It's their godamned uniform. And it's not Genderswapped. >.O WTF is wrong with you people tagging this, watch the show! The picture is just drawn with a feminine touch!

BTW, no sorry, Rei seems rather gay until the father/son relationship is explained but no, neither are gay. Though Yzaks a fucking psycho.

I don't remember skirts and thighhighs being part of Yzak's uniform.

Yeah, while the Zaft elite pilot dudes or whatever have a trenchcoat-like thing for uniform which you could use to explain the 'skirt', I don't think tighighs are a part of their official dresscode.

Tagging as genderwap because the pic is really effeminate even with the lack of chest. If someone feels that crossdressing would make more sense, feel free to, uh, state your case or something.