My 2nd commission for DeviantArt user, JR-95, we have a flat-color double portrait of his characters Adrianna, a mermaid, and Tommy, a young boy Adrianna befriends, and who ends up losing an arm that must be rebuilt using Mermaid technology.
Just like with my fanart, I wanted to elevate the original character designs by adding textural details and dimensionality wherever I could. This was especially true with Tommy's mechanical arm, which I changed up to be an armored gauntlet and pauldron, possibly taken from some old merman soldier. Gives the arm a greater degree of story and history. I also think this piece benefits from being in flat colors, because then the shading doesn't have to be too realistic, which might detract away from their features.