The Arisaka sisters (Hatsune and Kazuki) and the Kagura siblings (Yuuji and Marie) lived next door when they were smaller. So close that they could climb onto each other's verandas from the 2nd floor. They would always play together until one day the Kagura siblings had to move.
It's been 10 years and the Kagura siblings are moving back! Yuuji's turned into a pervert and Marie isn't the crybaby she used to be?

Shuuya Inukai is a model student at a high school who one day attracts the attentions of an ojou-sama, Kantori Isuzu, when she realizes that he is bearing, on his forehead, an X-shaped scar...that was also present on her pet dog's forehead...which leads her believe that Shuuya is actually the reincarnation of the said animal. And now Shuuya's days as Isuzu's pet begin.

All of the girls at his college love Suou Tsukasa and come up to talk to him on a daily basis. Unfortunately for them, Tsukasa hates girls that are straightforward like that, but is too nice of a guy to tell them that.

In fact, he has a crush on Kizaki Megumu, his classmate and one of the shy and least talkative girls. The professor in one of the classes they have together is Dr. Hime, a young teacher whose childish looks and short height makes her a target for her students to jokingly tease and treat her more like their friend rather than a professor.

After taking home the drunk Dr. Hime, who was served lots of alcohol by her students, Tsukasa learns a giant secret about her love life.