Tsuki no Ura wo Koete: Omegaverse

Mr. Tsukigase is known to have an "iron mask." He is expressionless and never smiles. Lucky for Hinoura, he gets to spend all summer with him in supplementary classes thanks to his grades suddenly dropping in the past semester. Hinoura struggles to concentrate and feels sleepy all the time, but for no particular reason... or so he thought. When Hinoura finds out that he's... not like the others... maybe he should stay away from Mr. Tsukigase... if he can, that is.

(Source: Fantasista Inc.)