An older male teacher at Futatsubashi Elementary School. The only one of the four main teachers seen in the series with children, specifically a daughter, Oyajima has an easygoing outlook on life and teaching and frequently dispenses advice and words of wisdom to his younger, more easily excitable work colleagues. Rarely flustered, he is the senior of Sae Sharai and has a visible soft spot for her, often offering insight to Hōin concerning their mutual colleague's behavior, background, and mindset in his usual, laidback style without coming off as defensive or biased. His good working relationship with Shirai also allows him to present her with alternative points of view or make thought-provoking observational comments in a gentle, nonconfrontational manner without either one of them getting worked up in the process.

3rd grade teacher Aoki Daisuke didn't expect the first class he ever taught to be one of the toughest obstacles of his life. After getting off on the wrong foot with the entire class, a moment of kind-heartedness instantly convinces one of his students, Rin Kokonoe, to make the ill-fated Aoki-sensei her lover. But what exactly are Rin's intentions for wanting to actively seduce Aoki-sensei, and will Aoki-sensei be able to help her to deal with them?

The story of Kodomo no Jikan is centered around 23-year-old Aoki Daisuke, who has just landed his first teaching job as a grade school teacher at Futatsubashi Elementary School. He is placed in charge of Class 3-1, where one of his students, a mischievously precocious Rin Kokonoe, develops a crush on him and goes so far as to proclaim herself Aoki's girlfriend. She aggressively pursues her efforts to be with her teacher despite the fact that he will lose his job if she gets too close, a situation further complicated by the often complex, intertwining relationships existing between them and their respective friends, families, and peers. 
(Source: Wikipedia)

A series of OVA episodes released with the limited edition manga volumes. Episode 01: What You Gave Me (Anata ga Watashi ni Kureta Mono) 
Kokonoe, Usa, and Kagami go shopping for a present for Sensei. Eventually Kokonoe decides to make one and they all end up spending the night at her house. Along the way we learn more about Usa's love for Reiji, Kagami's love for Kokonoe, and Kokonoe's love for Sensei. Episode 02: Kuro-chan, Shiro-chan (Kuro-chan to Shiro-chan) 
Kuro-chan tries to become friends with Shirai-sensei. Episode 03: A Child's Summer Time (Kodomo no Natsu Jikan) 
The girls, Aoki and Houin go into the country to visit Aoki's family.

Kenta Oyajima