Only the Ring Finger Knows(2001)

Sono Yubi Dake ga Shitteiru

At Wataru Fujii's high school, it's all the rage to wear paired rings with the girl you love. Wataru wears one though he is single, and one day inadvertently discovers that his ring pairs up with that of tall, handsome and smart Yuichi Kazuki, the senior classman idolized by the entire school. Though Kazuki has a reputation for being kind to all, when dealing with Wataru, he is strangely harsh. Their paired rings somehow draw them together and the two alternately clash and attract, as they must sort out their budding feelings for each other.

(Source: DMP)