Hazel Grouse is a character who appears as a foreigner from the wealthy Western continent, having crossed the ocean to reach Togenkyo. He is a young man with silver hair, blue eyes, and a generally neutral expression, dressing in attire reminiscent of the church while claiming to be an exorcist. His speech is elaborate and carries the specific intonation of his homeland.

At first glance, Hazel presents himself as refined, elegant, and soft-mannered. Beneath this composed exterior, however, he is deeply self-confident to the point of arrogance and has a talent for rubbing people the wrong way. He considers himself an intellectual and possesses both sharp intelligence and high physical capabilities. His most defining trait is a profound and persistent hatred for youkai, whom he refers to as monsters. This prejudice stems from his childhood, when the man who was both a father and master to him was killed by youkai. This event planted a deep need for revenge within him, leading him to follow in his master's footsteps as an exterminator of monsters. Hearing from the character Ukoku that Togenkyo was now under the rule of youkai, Hazel traveled there with the singular goal of eradicating them all from the land.

Hazel's role in the story is that of a major antagonist, driven by his uncompromising mission. He is particularly affectionate and respectful toward the monk Sanzo, believing they share similar pasts and trying to connect with him. In contrast, he harbors a secret cat-and-dog relationship with the three youkai in Sanzo's party, especially Hakkai, and refuses to address them by name, looking down on them with great distrust.

A key relationship is with his bodyguard, Gat. Despite communicating with him in a cold manner, Hazel shares a very strong and complex bond with Gat. This relationship is central to his character's tragic development, which differs significantly between the manga and the Reload Gunlock anime. In the anime's origin, Hazel's relentless killing of youkai led to him being punished by being transformed into one himself, which caused him to kill the priest who raised him. He was eventually killed by Gat under orders from the Great Spirit, but Gat, feeling sorry for him, chose to share his own life energy to revive Hazel. This act also gave Hazel's mystical amulet its power, but resulted in Hazel's memories being altered to make him believe he had killed and revived Gat instead.

Hazel's development culminates in the series finale, where his internal conflict reaches its peak. He attempts to kill and then revive Sanzo to force him into joining his crusade to wipe out all demons. During the ensuing battle, Gat is fatally wounded and, before dying, reveals the truth of their past to Hazel, causing him to regain his true memories. Defeated and overwhelmed by the realization that he has wasted his life, Hazel asks Sanzo to kill him, a request Sanzo ultimately grants after offering him a small measure of comfort.

In terms of abilities, Hazel possesses a special and powerful technique that allows him to replace souls. Using his golden amulet, he captures the souls of the youkai he defeats and uses them to revive humans who have died from youkai-inflicted wounds. The amulet itself is a crucial tool capable of storing these souls. While the origin of this power is unknown in the manga, in the anime it is a direct result of Gat's sacrifice, which also allowed the amulet to hold a seemingly infinite number of souls. Beyond this supernatural ability, Hazel is a skilled fighter who practices Western-style exorcism and boasts high physical prowess to complement his sharp intellect.