Anime waifus with a diverse range of victimhoods. You need the fat black wheelchair bitch, the autistic transgender muzzie girl, the inbred with literally no limbs. The possibilities are endless.
Whatever the gacha is, make at least 12 color variants of each one, in increasing rarity and exclusivity. Neckbeards will pay to have that rare gold foil purple edition.
What about a gatcha where everyone gets their own card or whatever the characters are represented as, the more you spend the more rare and powerful your card is, so the more others want to pull your card to use in battle, and the more famous in this gatcha you will become.