Mukuro Ikusaba (female) is giving Makoto Naegi (male) a reach around hand job underwater; he is mid orgasm. Mukuro is wearing the black and white bikini in the picture below while Makoto has plain yellow swimming trunks that are at his knees. Mukuro is leaning against him while jerking him off, with her chest pressing against his back (Smaller sized boobs). She's a few inches taller than him.
Makoto is blushing and flustered while Mukuro has a poker/straight face, although blushing a bit as well. There's a thought bubble from her that reads "He can't know how much I'm enjoying this..."
This is located in the ocean of a beach with the water reaching around their stomachs.