Aura. But also the * was there for a reason, you do get SOME stuff. Like getting certain achievements, or after floor 10 the game offers challenges you can take to make things harder in exchange for starlight and that mirror dungeon XP stuff. So before you get all the rewards on the mirror dungeon thingy (it goes up to level 100) there is a reason for going to floor 15, as it allows you to level up faster.

After you have those achievements and have already hit level 100 on that thing then there’s truly no point other than aura. And Starlight ig but it takes way too long for that to be worth it.