In high school, the big trend is to wear matching rings with your significant other and Wataru Fujii wears one too, even though he's single. Stuck with a hangover after a night of drinking, he goes to wash his face and takes his ring off so he won't tarnish it.
This is where he meets Yuichi Kazuki, a popular (and handsome!) senior, well-liked by the rest of the student body. Known for being extremely nice and friendly, Wataru is slightly taken aback by Kazuki's seemingly cold reception of him. It's not long after that they discover they have matching rings!
There is also a novel version of this.
WARNING
While there is not any explicit content, this manga does portray a homosexual relationship. If that kind of stuff bothers you, don't read it.
