I read this several years ago, and my search attempts on this site and google haven't helped me re-find it...

This girl and her friend get a job at a hotel/onsen. Things go wrong, but then the protagonist turns into a scantily-clad heroine who manages to save the day. If you're familiar with Hentai Kamen, the girl's clothes resemble a female version of that. The final boss battle involves a woman who enjoys putting mentos and coke up in her nether regions. It's not a hentai or smut, at least it wasn't labeled one when I read it (ecchi). But it could possibly be labeled as one.

Any ideas?

Yarisugi Companion to Atashi Monogatari

~4400 manga completed
~1700 ongoing...

Thank you!