Itsuki serves as Sensui's closest ally and right hand in executing his master plan. While he's got serious psychic powers himself, he needs someone who can tear through dimensions—something only Kuwabara can do in the human world. That's the key reason Kuwabara becomes essential to their scheme.
The origin of their partnership is oddly touching. Itsuki, a demon at the time, challenged Sensui to a fight and lost badly. He was completely outmatched and at Sensui's mercy, facing death as just another demon target. Before the killing blow, Sensui offered him a final wish. Itsuki asked for one more day of life so he could watch the last episode of his favorite TV show—which turned out to be Sensui's favorite too. That shared moment basically cemented their bond, and they've been inseparable ever since.
What's fascinating is how the series shows Itsuki's devotion through his constant observation of Sensui. He watches everything—his movements, his emotional states, his fighting technique, his weaknesses. There's an intensity to how he studies his companion that goes beyond simple loyalty.
Content compiled by AnimeList.moe from publicly available sources.
