Aozora no Sunda Iro wa Manga澄藍色的戀空; 青空の澄んだ色は; The Color of the Clear Blue Sky
From Attractive Fascinante:
Aiming to become a sensei like his former sensei, Sugiura Sakae came to an elementary school as a contract teacher. Coincidentally, his former sensei, Fukada Ryuuji, is currently teaching here. Ryuu sensei is Sakae’s idol as well as his pillar of support. However, the “Ryuu-sensei” he once so admired, is totally different now. Feeling bothered, Sakae slowly realizes that his feelings for sensei have become love. But what about Ryuu-sensei?.