How far do the hidden quests go?

For now, I'm challenging the hidden quests up to rank 70. I'm debating whether to stop at rank 70, but I wonder how far they actually go... I'm trying to stop before the urge to spend money grows, but I'm still thinking about it. It's not that I'm particularly invested in the story or want to beat someone, but the characters are so cute that I'm tempted to pull on the gacha~ (´-`).oO I'll be thinking about it while playing today too.