Mahiru and Kuro are getting absorbed into the team M polycule
I think that they all would get along really well. Like genuinely once they sort through the things they've done to each other during the war, probably starting with Kuro apologizing for nearly biting Belkia.
And poking a hole in his hat, which may be more unforgivable.
Team M by themselves have a variety of different personalities and different interests so it's not so out of the blue to have Mahiru and Kuro's personalities and quirks to the mix. And even then, the usual trauma that surrounds any of the Melanchonies actually still somewhat applies to the both of them; Mahiru who has suicidal ideation and would rather die than be alone again and Kuro who, pre-realizing he needs to help Mahiru like he helped him, would have taken any chance to die and stay dead.
Also all having beef with C3 in some form or another is something that can tie them together rather nicely.
Kuro would be far more awkward with the Elites than Mahiru would simply because he's just like that but he's gonna try.
Kuro recommending good games to Sakuya, Belkia and Otogiri. He learns and factors in their taste. He keeps beating Belkia in Mario Kart and he gets all pissy about it.
I hc that Kuro is more creatively inclined and writes/has written so once that fact slips out he and Higan have at least a little something to talk about (Art, meaning. The artist and writer friendships are real and Strong.)
Mahiru and Shamrock joining together in their housekeeping skills. Mahiru's apartment and Tsubaki's penthouse have never sparkled more. Going grocery shopping together and teaching/learning tips and tricks. They get along swimmingly.
Kuro @ Shamrock: Damn theres two of them now
Belkia and Mahiru is something im not yet sure what to do with but we'll get there.
Otogiri and Mahiru would work and it'd start when Mahiru asks about her thread/string and Otogiri answering questions which leads to the both of them sharing pictures of their latest sewing projects.
Kuro and Otogiri would chill but also she thinks his kitty form is really cute and wants to pet him. It takes a bit but Kuro eventually allows it willingly.
Mahiru and Higan just Works. Somehow. They def get along better than Higan and Sham so theres that at least.
Sakuya's getting smooched either way by everybody so its all good ww