Only the Ring Finger Knows - Novel Series by Satoru Kannagi

It's the ultimate expression of love to wear matching rings with your significant other, showing the world that you are a couple. High school student, Wataru Fujii, also wears one even though he is single. When he accidentally switches rings with a popular and handsome senior, Yuichi Kazuki, they discover that their rings pair up! Since that moment, Kazuki - who is known for being kind to all - becomes strangely harsh to Wataru... moreIt's the ultimate expression of love to wear matching rings with your significant other, showing the world that you are a couple. High school student, Wataru Fujii, also wears one even though he is single. When he accidentally switches rings with a popular and handsome senior, Yuichi Kazuki, they discover that their rings pair up! Since that moment, Kazuki - who is known for being kind to all - becomes strangely harsh to Wataru. They alternate between hot and cold, as in between clashes they begin to sort their feelings for one another. Are Wataru and Kazuki the worst of enemies or are they actually soulmates? less

Yuichi, who has just been accepted into an extremely prestigious national university, has planned a vacation for his exam-ridden boyfriend, Wataru. Looking to raise money for the trip, Yuichi agrees to a short-term job with his college senior Asaka, whose cool attitude and mature personality makes for an uncanny resemblance to Yuichi himself. Taking a liking to Wataru, Asaka makes no effort to hide his interest and advances. How long will Yuichi be able to contain his frustration and jealousy?

After all the studying he did for his exams, sacrificing time with his boyfriend Yuichi, Wataru gets a measly C-average on his summer prep test. Yuichi's college classmate Asaka offers to tutor him, and he eagerly accepts. Wataru finds Asaka's cool beauty and attitude strikingly similar to that of Yuichi's, and subconsciously becomes vulnerable to his advances. For the first time in their relationship, Yuichi becomes enraged. Will they be able to overcome this new obstacle?