I will answer your question despite the fact I’m not Pachi: First: there are only 5 scenes Second: you can go to the bathroom. If her lust meter is high, you can walk in. If not, uh I haven’t tried yet. And **Mayu is not your girlfriend. It’s your sister **. For greater details, please go read the v0.05 update log. The mental meter doesn’t have much use now. You can’t increase it. You can decrease it, but I’ve only did it once (you force her to show her panties and after that, the lust meter becomes high enough so she shows you her panties without forcing)
There is a meter at the left top of the screen. When she gets naked, you’ve fulfill it. For mental scale, you pretty much can only do it once since after that, her lust meter becomes high enough for you to not force her. Her mental bar decrease when you force her. Again, I’ve only done it once (and lol it’s her underwear, not yours). Maybe pachi didn’t respond cuz i did all the work…