Itsuki is a demon who grew fascinated by the Human Realm's newest Spirit Detective Shinobu Sensui, he then began to follow him and assist him from the shadows. However once Shinobu found out he nearly killed Itsuki, but spared the demon after he made him laugh. He then begins acting as a partner to Shinobu in his cases, while falling in love with the Spirit Detective. Once Shinobu was diagnosed with his disease Itsuki joined the Sensui Seven to assist in the plans, actively working on opening the tunnel to Demon World. Towards the end of the arc he captures Kuwabara, Hiei, and Kurama in his alternate dimension forcing them to watch as Yusuke Urameshi and Shinobu begin their battle. After Yusuke's death, the group's power jumps to an A Class, allowing them to escape their prison and begin a battle with Shinobu in Demon World. Following the resurrection of Yusuke Urameshi and his new Demon Energy and the death of Shinobu at his hands, Itsuki travels to Demon World. Once their he puts Yusuke's guilt to ease with the knowledge that Shinobu would have been dead in a month, and he then refuses to allow Koenma to take Shinobu to Spirit World and judge him, pulling his body into his dimension so the two can spend eternity alone together.
Powers and Abilities
Itsuki possesses the ability to travel between dimensions. He can also summon a demon with which the inside of which is another dimension, where he can keep his prisoners.