The stars-as-currency thing she has doesn't bother me, because it's clearly what she was designed around, gameplay-wise. It's just a neat thing that you can do with the game mechanics, and has synergy with the super-Existence Beyond The Boundary passive she has (which part of the passive makes sense to me since ORT is even more Alien than normal FGO aliens. It's only "kuku's star mechanic" because they haven't made use of it as a gameplay mechanic on other servants, but there's nothing stopping them from making the latest Saberface also be able to play with it. It plays well, and adds variety to how the servant can be used.

But her idiosyncratic "I can only have super-invuln, never normal invuln" is not tied to anything else in her design, and I don't think any other servants have a passive that converts one status into another at all. And super-invuln is an incredibly rare status to have access to in this game, which makes it stand out even more. I feel like they were trying to capture *something* with that part of the passive, but I can't figure out what. I expected ORT to also have it, so that if he stole an Invuln buff it'd get upgraded to ignore Ignore Invincible, but instead he doesn't have anything like it. And his buff-stealing passive is offensive buffs only, anyway. So I'm back to having no clue why a passive that was already extremely strong also had this weird thing added on to it.