>>50187597Only Serena is in character in that pic, her lusting hentai style after Ash is literally canon so yeah.
Dawn would probably not be thinking about the sexual at all and if she would it would probably be sth like her randomly reminiscing about her sex with Cynthia (Dawn living at Cynthia's house in Unova in BW is also canon).
May would probably be nostalgic about Drew, or secretly happily thinking about how jealous Drew would get if he saw her with Ash or sth like that. Drew is definitely top priority for her.
As for Ash, the only girl in canon to make him semi aroused was Giselle so I assume Giselle is the one taking the photo.
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That's a more ashnime canon interpretation, of course, in the OP's fanficverse, Ash is probably an omnivore fuccboi like Brock, Ash fucks all his female companions in this "universe".