Dia Kurosawa's strappy bikini/swimsuit from this Dengeki G's poster. It's somewhat of a meme in the Love Live community, to the point where it has enough fanart to train a LoRA of it. The Umamusume fandom also seems to have adopted it (on Silence Suzuka for some reason).

In any case, the unique trigger is "diakini". Strengthen it with "red bikini, print bikini, multi-strapped bikini" – If you really want to go ham on it, there's possibly several more, go to the Danbooru link above to see them all. The original design also comes with a "thigh strap" and "jewelry, bracelet, sandals, cross-laced footwear", you might have to put these in the negative if you don't want them or in the positives to guarantee them. And of course, there's the official Booru tag "kurosawa dia \(dengeki g's poster swimsuit\)", but that doesn't do a lot for the bikini on its own (hence this LoRA) and also obviously implies a lot of Dia, which may or may not be what you want.

It seems to work well with color changes, obviously change the "red bikini" part for that. It does not work well with wild skin color changes, not showing a lot of skin to begin with, or getting any image rating lower than R on CivitAI. Because it's a bikini.

Pro tip: "skindentation" is nice tag to use with this, or just in general.