>>43129070Realistically? Kinda like this-
It really depends how the situation would play out at the start. I mean even in the show itself, Serena is shown to be effectively a teenage girl with raging hormones(her weird reactions to both Ash and Millfeui's touches give us reason to think that Serena is biologically bisexual, as in her body is physically attracted to both men and women even if she doesn't realize it consciously herself) so if Ash non chalantly says something like, " how about you, me and Dawn have sex in a threesome" she'd probably agree fairly easily, albeit with some hesitation but she'd still agree and only realize the bisexual implications only AFTER the sexual act.
But if Dawn brings up the threesome topic by herself, Serena would turn down the request immediately and get mad or sth. She'd think of Dawn as a slut or something along the lines in accordance to her own vocabulary.
If for some reason Serena started having such fantasies independently, she'd still be to prude(unlike Millfeui who seems to be much more confident and aware about her desires) to bring up the topic to
Ash,
who is written so inconsistently at this point he's pretty much an OC which you could give a wide range of somewhat suitable reactions and they wouldn't feel out of character because his character is not wholesome and well defined anymore post DP. Of course there still are things Ash would never do or ways he'd never react.