Leo! Likewise Percy hasn't had a bunch of interaction with him, and he was kind of sus with their whole first meeting. BUT having since been possessed, he totally gets what happened, and honestly, he really likes the guy. The whole prankfest has only confirmed this in his mind - Percy likes to be able to let go and have sometimes, and Leo operates on his wavelength wrt that. He does think that he needs some serious help with the ladies though, because dude. It's quality, not quantity.

THERE IS ONE THING that Percy would probably side eye Leo on and that's Hazel, because Frank is his bro and Hazel is his babby sister, but that's not likely to come up for a bit so Percy will legit just put it to the back of his mind and forget about it, because he's oblivious like that.

At the end of the day Percy's basically been through this whole world-saving shtick before and he knows they won't get through it unless they work together. I think that by virtue of being one of the seven, Percy's basically already accepted Leo into his demigod family even though it's only been like LMAO less than a month. Which is part of the reason why he's so willing to engage in prank wars and other stupid things - he's not really the sort of guy to do that sort of thing with someone he didn't consider a friend.