All plugins used are listed in the Credits.txt file.
The trick is to not expect a pre-baked solution. You're obviously never going to find a plugin that does all of the stuff for say sex combat out of the box. You have to figure out what you want to do, break it down into smaller, more innocent pieces, and then look for a plugin for each of those. Switching sprite sheets, for example, is absolutely something a lot of rpgs do for powered up states and so on, so there are a number of plugins to help with that. I forget the exact one used here, but again, dig through the Credits file, it's in there.
And then of course it's all held together with a bunch of in-engine scripting, which is kind of a rats nets because of how spread out everything is in RPGmaker. But it works.