Only the Ring Finger Knows

Only the Ring Finger Knows (その指だけが知っている, Sono Yubi Dake ga Shitte Iru) is a shōnen-ai light novel series written by Satoru Kannagi. It was made into a manga illustrated by Hotaru Odagiri, which has been licensed in the United States by Digital Manga Publishing.

Plot
In the school that Wataru Fujii goes to, when one wears matching rings on their right middle finger it is a sign of friendship, a ring on the right ring finger means single, and to wear matching rings on the left ring finger means a couple. One day Wataru accidentally switches rings with the very kind, handsome, popular senior, Yuichi Kazuki, because for some strange twist, their rings match. For reasons that Wataru doesn't understand, Yuichi becomes uncharacteristically mean to Wataru. After this strange incident, Wataru and Kazuki happened to meet more often, starting an electric relationship around the matching rings. Wataru starts to wonder why Yuichi’s mood towards him switches to sweet-teasing to evil: is it because he just can't stand him or is it because he actually loves him?

This meeting of two students that everything seems to oppose, will led to the birth of an unexpected secret that only the ring finger knows.