This is a fanart of Fai D. Flowright, of Tsubasa Reservoir fame. However, this particular Fai comes from an alternate universe fanfiction by CLAMPraven. This story is named Siren's Cove and is one of the best (yet unfinished) stories I have read. In it, Fai is a merman (of a sort). At one point in Chapter 4, Kurogane paints a portrait of Fai. This is what I believe the portrait would look like.

I tried to stick to what was given about the portrait (mainly torso, pink sunset, Mona Lisa smile) while still putting in my own interpretation of the character. I tried to make it look more like an oil painting than my usual work, which is why the colors aren't as blended as I usually try to make them. I don't know if I succeeded at this. I do like my conversion from anime-esque to a more realistic form. I also like the smile...love the smile. A bit wider than the Mona Lisa's smile, but Fai has a wider-than-normal mouth.