Mayuru Oni wa Ao ni Tsukafu

In a world where yokai live among humans in disguise, there exists a shrine known as the Sakamori which is tasked with guarding the boundary between humans and spirits. Kotaro, a misanthropic demon, enters the service of the Sakamori on his twentieth birthday. His master, Yushin, is a human who looks frail and defenseless, and life with the gentle shrine keeper seems a little dull at first. However, after a certain incident, Kotaro suddenly goes into heat… "Your demon is suffering, you know. If you're Sakamori, you'll do something about it, won't you?" Trying to quell the smoldering heat inside his body, Kotaro throws these provocative words at Yushin… (Source: Coolmic)