Uhhhh.... idea, I guess:
- Thinking of the alchemy idea above, detach the Suika part of the game from the girl expansion part, two separate entities within the game.
- The Suika part is how you collect chemicals to work with, every merge gets you research towards that chemical and produces the larger ball, and if that larger ball merges, you get research towards the second chemical and so on.
- Research a chemical enough and you get it for the alchemy minigame. (Dunno if it'd be "[#] merges = 1 use" or "[#] merges to unlock [chemical] forever" though.)
- Easy chemicals are the fodder, you get tons of them and they're more like "currency" for the alchemy, the more you dump into a potion, the more effect it has, up to a certain limit so you can't one-shot the growth. (Maybe there's a potion size upgrade in the shop?)
- Higher-tier chemicals are the "blue + yellow = belly / green + cyan = futa" type stuff, the baseline ingredients to make the potions, the ingredients you need to experiment with.
- Merging the biggest balls could result in a multiplier ingredient that makes potions way more effective, or it's some special ingredient that turns a potion into a max size increasing potion
- Once you've made a potion, it saves the recipe in a list so you can make it again with one click.
- Every character has different reactions to different potions, so you have to start the alchemy minigame testing over from scratch each time, so what might be a boob potion for one character could be a belly potion for another.
- Could pad out the recipe list and save a lot of time by including hair color potions, or having growth/shrinking versions of the potions be two separate recipes.