Azuma has been tasked with taking care of his sister's son, Taira, while she's overseas for a couple of weeks. Azuma is ditzy and doting to his nephew. You can already tell within the first two pages that Taira has a crush on Azuma. When the mother comes to pick Taira up, she tells Azuma that they're going to be moving overseas. Taira hadn't mentioned this to Azuma so he was pretty shocked. He asks that they visit sometime and Taira says he won't until he grows taller than Azuma and kisses him. Four years pass and Taira has come back, much to Azuma's surprise considering Taira has grown into a tall hottie and so unlike his cute nephew.
Taira constantly tells Azuma he loves him, but Azuma believes he only means it in a platonic way. It's spelled out clearly when Taira says that he wants to have sex with Azuma. Taira is persistent to get Azuma to understand his feelings so when they finally get across to Azuma, Taira kisses him. The kiss gets heated and they end up having sex. Afterwards, Azuma goes to Taira's apartment (which is right next door to his) and locks Taira out to freak out because he thinks he failed as an adult/uncle. He notices lots of pictures of himself in Taria's apartment and his glasses that Taira took before he left for England. Taira breaks into his apartment and they have a chat where Azuma finally realizes how much Taira loves him and they live happily ever after.
Mayonaka no Oyatsu