I personally think that the term soulmates works for the relationship between Iruma, Clara, and Asmodeus, even in a purely platonic sense. That's just how close the trio feels to each other.Best Friends also works, but I imagine why the tl team didn't use that term is because the meaning of that term is self-evident if you know what friends are. Maybe confidant would have worked too, but that's too professional IMO. I wouldn't exactly describe the relationship between the 13 Misfits that way, but comrades feels like a fitting term.