>>715192184
The main stat you need is APL, so since you're asking, I'm assuming you don't have any sort of build (and it's sort of dumb to have one anyways, when butt battles happen like three times a year or something and it'd take a lot of resources to fully set up for it)

In your case, the best option if you can would be to use a girl that you have an APL suit for, since they have 550 or 600 APL.
If you have some, equip APL decos on her as well. For PP skills in accessories, either try using APLs, or try POW/TEC (don't use STM for this since it does nothing in butt battle)

The reason for all this is higher APL = more tension bursts, and butt battle rules are set up to heavily favor the tension bursts.
The shop should also have the Top Coats which you can use to raise your girls' APL stat permanently by 30 or 40, (Depends on the girl, it's set up so it balances out at the end. Girls with default 10 APL can raise by 40, with default 20 APL can raise by 30)

This is specifically for butt battle btw. Regular matches calculate score in a different way, so APL builds aren't as effective there.