Random ideas to potentially use at your call;
1. Voodoo Doll item. you buy it from Dalvie, and you can give it to any of the major NPCs. From there, it works like the Meat Parasites/Cursed Underwear, randomly increasing your ERO gauge (or decreasing your stamina, in the case you give it to Alissa or Bell) with little bits of flavortext depending on who you gave the doll to. I'd imagine that the status would be easy-ish to program, given the similarity I'm imagining with status effects that are similar? But I don't use RPG maker MV enough to know
2. The thing that happens when you max your ERO gauge with the hypersensitive nipples cursed bra combo happens on the next tick when you max out your ERO gauge with any ERO-bar-increasing equipable. (This is mostly because this idea is very appealing to me)
3. Gambling Minigame on the Island, maybe? I think there being Strip-Poker on the island would be very fitting for it
4. An enemy that inflicts a Bleeding/Bloodsoaked status effect, I just think it'd be interesting to see how the NPCs would individually react to you strolling in covered in blood