The Color of the Clear Blue Sky(2007)

Aozora no Sunda Iro wa

Sakae Sugiura wants to become a teacher, and finally gets assigned to an elementary school. There, Sakae reunites with Ryuuji Fukada, who was his teacher when he was a student there. Sakae always looked up to Fukada, who acted like a life-support for him at times. Their meeting again surprises Sakae, and he feels hesitant due to how much Fukada seems to have changed. But then, his feelings toward Fukada gradually change...

(Source: Renta!)