unfortunately, the only grinding aspects of this game thus far:
- the RNG for getting the girls from bosses
- 12 hour wait for shop updates, where you buy out all the girl affection and girl exp items
- energy use that's only used for missions

once you have caught up in the campaign missions, that's it. energy doesn't do anything else after that .
once you have obtained all the girls from the bosses, you can only spend your fighting stamina on pvp battles
once you have leveled all your girls to 3stars and level that matches your own, the shop no longer has a purpose

I only started a week or two ago and I'm already at this point. to be fair, I did spend 98% of my time grinding dark lord for the girl I didn't get. but after that there really isn't anything else left to do.

as the tower of fame doesn't do much other than compare you to everyone else, and the in-game currency pachinko doesn't really have a purpose???

because you're right, it's frustrating playing against a 1% drop chance. and currently all your girls can do outside of battles is supply money.

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TLDR:
while I do like all the effort they're putting into the campaigns, levels, story and art. I feel like there should be some system for grinding (using energy) after all the (non-premium) girls have been acquired.

though I guess sex gangsters didn't have anything else after that either. but they did have a system where you could get the same girl more than once and they merged giving them a sort of +1 to stats and such. if I remember right, there really wasn't a limit to that merging either.... hmm.

anyways, great job guys. keep up the good work.