The OVA is based (only small part of it) on a very popular manga from Ribon by the same title. The story focuses on relationship between Nao and Uehara. Nao lives far away from school, so she needs a nearby apartment from school. Lucky for Nao, she can live in an apartment with Uehara, a really popular high school boy.

But since they are going to the same high school and people will easily criticize that a high school boy and girl are living together, therefore Nao and Uehara tried to hide the fact that they live together in an apartment. It`s actually not hard if they don`t have romatic feelings toward each other, not to mention there are other people who have crush on either Nao or Uehara...
(animenfo.com)