Hazel Grouse is a character in Saiyûki Reload that started appearing at the "Even a Worm" arc.

He's a foreigner from the rich Western continent who crossed an ocean to visit Tôgenkyô. His dress is that of the church, but in actuality he follows in the footsteps of the man who was both father and "master" to him, and exterminates monsters. When he was a child, his master was killed by monsters, so he now holds in his heart a persistent need for revenge and a sense of hatred. He heard the story of Tôgenkyô from Ukoku, whom he met in the past. Knowing that Tôgenkyô is now under the rule of youkai, he traveled there with his bodyguard Gat in order to send all youkai into extinction.

He has a special revival technique through which he can replace souls. He uses the souls of the youkai he's defeated to revive those humans who died by youkai-inflicted wounds. It is currently unknown as to where and when he gained that ability. He has lost one portion of his childhood memories.

He is a beautiful young man with silver hair, blues eyes, and a neutral countenance, and he speaks elaborately with the intonation specific to those of the Western continent. At first glance he is elegant and soft-mannered, but is rather self-confident and is good at rubbing people the wrong way. In actuality he is an intellectual, with both sharp intelligence and high physical capabilities. He is affectionate towards Sanzou but with the other three youkai, especially with Hakkai, he has a secret cat-and-dog relation.

In the Reload Gunlock anime, Hazel has a different origin. He would often kill youkai, and was eventually punished for it by being turned into one himself, which resulted in him killing the priest who raised him. He continued killing youkai but was eventually killed by Gato, under the orders of the Great Spirit. However, Gato feels sorry for Hazel, so he then chooses to revive him by sharing his own life energy, which also gives Hazel's mirror the power to revive dead humans with youkai souls (in the anime, the mirror appears to be able to hold an infinite number of souls). However, Hazel's memories become altered to make him believe that he was the one who killed and revived Gato instead. In the finale of the series, Hazel attempts to kill Sanzou and revive him, in order to get Sanzou to join him in wiping out all demons, but Gojou, Hakkai and Gokuu intervene and Gato is fatally injured in the ensuing battle. Before dying, he reveals the truth to Hazel, resulting in Hazel regaining his own true memories. Hazel is then defeated in his youkai form by the Sanzou party, and feeling that he has wasted his life, then asks Sanzou to kill him. Sanzou complies with his request, though before shooting Hazel he comforts him somewhat by telling him that nobody wastes their life.[/spoiler]

(Source: Saiyuki Wikia)