Takeru and Kimihito have known each other ever since they were children. This is mainly because Takeru's family has long served Kimihito's family as their bodyguard. Kimihito relies on Takeru about everything, including masturbating since he didn't know how to do it when he was a kid. They started innocently when they were kids but they kept doing it even though they were already high schoolers. Takeru has been harboring some hidden feelings for Kimihito since he was a kid so he didn't mind doing everything for Kimihito (he actually had ulterior motives as well and there was a scene where he had thigh sex while Kimihito was sleeping)
The main issue is the presence of a person that likes Takeru who asked him to be his bodyguard, and Kimihito's concern of being a burden to Takeru
Ichinose-kun wa Itsumo Iinari.