Bisexual

The main character is Shichiri, who has an identical twin named Nanai. He does kendo, and in his first match as a little squirt he played and lost to a boy named Kitsuma.

Now, several years later Shichiri and his brother start middle school. Kitsuma is a third year student and openly bisexual. He teases poor confused Shichiri to death. Shichiri is in love with Kitsuma's ex-girlfriend, and torn between the two of them. But slowly he comes to enjoy his stolen time with Kitsuma more and more. And then their fathers find out and they stage a daring runaway. But was it really necessary?

(Source: Translated Treasures)