An older male teacher at Futatsubashi Elementary School, he stands out among the four main teachers featured in the series as the only one with children, specifically a daughter. Oyajima embodies an easygoing approach to both life and teaching, often sharing advice and wisdom with his younger, more excitable colleagues. Rarely ruffled, he serves as a senior figure to Sae Shirai and displays a noticeable fondness for her. He frequently provides Hōin with insights into Shirai's behavior, background, and mindset in his typically relaxed manner, without appearing defensive or biased.
Oyajima's good rapport with Shirai enables him to present her with alternative perspectives or make thought-provoking observations in a gentle, non-confrontational way. This approach ensures that neither of them becomes overly agitated during their exchanges. His laidback demeanor allows him to navigate potentially sensitive topics smoothly, fostering a collaborative and understanding work environment.
