Two things:
1. Shouldn't this be tagged as shota?
2. The inseki tag is misapplied; I'm pretty sure they're cousins, which qualifies this for straight up incest.
Hmm, so Akira-kun gets Miki-nee while Kazuaki gets the younger sister...I suppose that's fair enough, I do think the younger sister is cute too.
Great ending though. Well hey, it's great that they can soon be together more frequently than just occasional trips back during holidays.
Too bad, Kazuki-kun ... you get stuck with younger sister calling you: "Onii-chan". Meanwhile, Akira-kun Knows What Is Best In Life (Miki-nee) and *cough-cough* partakes of it to the fullest.