Well there is that too! Honestly I think you could take the four - Haru, Makoto, Rin, and Sousuke - and just make any combo and it would work somehow. Because yeah, like you said, Sousuke and Rin is pretty obvious, in a similar way that Makoto and Haru are. Plus Haru and Rin, of course. I think the only one I haven't read is Makoto and Sousuke, although I won't swear to it. Regardless, I am now so tempted to go look for some! Haha. :D