Gomen

Twelve year old Sei has hit puberty and is quickly becoming sexually aware, sometimes not as privately as he'd like; erections in school and other inopportune times plague him. He talks about it with his school friends, Kinta and Nyanko, in between their feuding over the affections of classmate Yumi, but can't figure out what to do about it.
On a day trip to Kyoto to visit his grandparents, Sei has a chance meeting with Nao, a strong-willed, dream-like girl, while waiting for service in a pickle shop. She quickly becomes the objection of all of this thoughts and desires, but there is one small problem: he doesn't know her name or where she lives. He arranges another trip to Kyoto on the next weekend and finds out her name, Nao Uryu, from the owner of the pickle shop, and starts an investigation around town of all of the Uryu families. He finds her working in her father's coffee shop, but his hopes are crushed when he finds out she is a year older and already in junior high. Sei is undaunted, though, and visits the coffee shop again, this time having a long and telling conversation with Nao's father while she is out visiting her mother. Upon her return, Nao and Sei take a walk around Kyoto, seeing the sights and talking. Sei, who forgetfully left his scarf in the coffee shop, is lent Nao's pink scarf for the walk. He waits for the day when Nao has to come to Osaka for the day to trade scarves so he can let her in on his feelings, but at the same time a girl at school is planning to do the same to him. - wikipedia.org