Though this is my first yaoi OTP (and generally, my first OTP ever), I would like to include some canon history! Kurama first met Hiei while he was attending middle school. Hiei had mistaken Kurama for one of Yatsude's servants (a demon who had been terrorizing the town). The two battled, but when Kurama realized Hiei's mistake, he stopped the fight. However, Hiei was injured. Kurama took Hiei back to his home and treated him.
Maya was a classmate of Kurama's during middle school. She openly admitted to being in love with him, and it's apparent that Kurama had the same feelings for her. Maya was kidnapped by the demon Yatsude and almost devoured, but Kurama and Hiei defeated Yatsude and rescued her. Later, Kurama erased her memory of the horrible events. After that, Hiei developed respect for Kurama and the two became friends for one year before teaming up with Gouki and stealing the three Spirit World artifacts.
He then becomes one of the three members in Hiei's Underworld crime ring, and steals the Mirror of Forlorn Hope. Yusuke Urameshi faces Kurama on his first case, which is to recollect the stolen Spirit World artifacts. However, Kurama does not fight Yusuke, for he is trying to use The Mirror of Forlon Hope to save his human mother, Shiori Minamino, from dying.
Their friendship remains true throughout the entire series, where their interactions seem to point out that Kurama is one of the few Hiei allows "in", and that Hiei is one of the few that Kurama can relate to.
Ironically, Kurama's name comes from the Kurama Mountain, in Kyoto, Japan. Mount Hiei stands right beside it. ♥