The perks were a new feature for P5. I missed them too, they gave much more of an incentive to hang out with certain people.
Here you just unlock the Arcana's ultimate fusion at Rank 10, and more importantly, stop them constantly pestering you to hang out on Sunday. There's no need to rush to 10 though, you won't be high enough level to actually fuse any ultimate until early 50s, and some of them even go into the 80s from what I've seen. Generally though, ones you meet earlier have lower level reqs.
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