I really like the girls' party quartet (ritsu, arashi, mika and mayoi)! I think especially when it comes to mika and arashi, they were both very important to ritsu's growth as an independent person. knights aside, the both of them can be considered some of ritsu's first actual friends, people he actually feels comfortable opening up to and relying on, for serious matters or just silly teenager things, like pajama parties. after only having mao by his side for so long, he found people who would actually care for him, understand him (sometimes in ways that even mao never could) and do their best to match his mood (that's why he feels so comfortable living with mika despite hating the idea of sharing a room with someone, as stated by ritsu himself).

other than them, I really like his relationship with anzu. I just find really really cute how they both became such close friends and how they rely so much on each other, to the point that even anzu, who's always trying to deal with everything by herself, will go to ritsu for advice bc she trusts him a lot as a strategist but also as a good friend. she's also not someone who shies away from his affectionate nature or his vampiric behavior (including his gorey jokes lol), and I guess that's very heartwarming for him, she's not only a competent producer but also someone who he can be himself with and he's comfortable around her. I really enjoy seeing their mutual trust in each other and how it was developed throughout the story <3