A story about a researcher in an abandoned castle, taking care of a mysterious egg. Everyone who used to work there has already left, leaving him completely alone. One day, the egg cracks—and as the only scientist remaining, he’s forced to raise the dragon (in human form), especially teaching him about sex education.
There are two seme in this story, A and B. While A is the same age as uke, B is younger than both of them. The uke, A, and B were childhood friends. The uke secretly loved A and confessed, but A rejected him harshly. Heartbroken, the uke left for another city but later returned broke. Back in the village, both A and B started pursuing the uke, who was still confused and trying to forget the past.
In the Castle: the Dragon's Erotic Education