Rumi and Naori are twins but have nothing in common, except their feelings for Jun, their next-door neighbor.

After dumping Jun, Rumi makes another request of him, one that he couldn't have seen coming.

Jun decides to help Shiena with her studies, which drives Naori crazy. Rumi, on the other hand, seems unusually indifferent about it. However, for Naori, it's clear that she needs to keep an eye on them. So, she quickly invites herself along.