Cho Hakkai, originally born as Cho Gonou, is a central figure in the Saiyuki narrative. His past is marked by profound tragedy and loss. As a human, he was a quiet and intelligent orphan who felt disconnected from others. He was eventually reunited with his long-lost twin sister, Kanan, with whom he fell in love, unaware of their relation at first and later accepting the complex bond. They lived together until Kanan was offered as a sacrifice to the demon Hyakugan Maou by the villagers to spare their own. Consumed by rage, Gonou slaughtered not only the villagers who betrayed her but also proceeded to kill a thousand youkai in Hyakugan Maou’s castle to rescue her. Upon finding Kanan, she tragically took her own life. As a result of bathing in the blood of a thousand demons, Gonou himself transformed into a youkai. He lost his right eye during the ensuing confrontation. Left for dead, he was rescued by a stranger, Sha Gojyo, who took him in and helped him recover. After being tried for his crimes and given a second chance by Genjo Sanzo, he abandoned the name Cho Gonou and took on the name Cho Hakkai, signifying his new beginning.

On the surface, Hakkai is the epitome of calm, politeness, and level-headedness. He is the most rational and peaceable member of the Sanzo party, often acting as the mediator who smooths over conflicts and handles practical matters like securing lodging and supplies. His ever-present, gentle smile is his most recognizable feature, but it often serves as a mask to hide his deep-seated pain, guilt, and self-hatred. He can be prone to making disturbingly cheerful remarks or telling frightening stories with a straight face, which unnerves his companions. Despite his friendly demeanor, he carries a heavy burden of remorse for his past murders and harbors a strong hatred for youkai, a hatred that extends to his own transformed self, which he views as a form of punishment.

Hakkai’s primary motivation is one of atonement and protection. He is driven by a desire to ensure the safety and well-being of his new family, the Sanzo party, as a way to make up for his failure to save Kanan. He is fiercely protective of his friends and will go to great lengths to shield them from harm, often putting his own life on the line. While he has seemingly made peace with his past, his actions are heavily influenced by a need to prevent further tragedy and to prove that he is no longer the man who committed those terrible acts.

In the story, Hakkai serves as the team's healer, driver, and emotional anchor. He is the caretaker who cooks, cleans, and looks after the group's basic needs, earning him the role of the "team mom." He is the one who keeps the bickering trio of Sanzo, Gojyo, and Goku in check and represents the group's conscience and strategic mind. His pet dragon, Hakuryu, transforms into a jeep, which Hakkai drives throughout their journey.

Hakkai’s most significant relationship is with Sha Gojyo. Gojyo is the man who saved his life and gave him a reason to live. The bond between them is exceptionally deep; they are best friends and roommates who understand each other implicitly, often communicating without words. Gojyo is the only one who can consistently see through Hakkai’s smiling mask, and Hakkai has proven he can pull Gojyo back from the brink of despair. His loyalty to Gojyo is unwavering and arguably surpasses all other connections.

With Genjo Sanzo, Hakkai shares a relationship of mutual respect. They are the two most mature members of the group and often serve as each other's confidants. Sanzo was instrumental in sparing Hakkai’s life and in giving him a new purpose. Hakkai is one of the few people who can speak with Sanzo without being threatened. With Son Goku, Hakkai has a warm, mentor-like bond. He indulges Goku's childish appetites but also teaches him important lessons. His relationship with the demon Yaone is more nuanced; he sees a reflection of his lost love, Kanan, in her, which leads to a sense of kinship and a desire to protect her.

Throughout the series, Hakkai shows significant personal development. He begins as a broken man consumed by guilt and passively seeking death. Through his interactions with Gojyo, Sanzo, and the others, he gradually learns to value his own life again and re-engage with the world. He transitions from being "Cho Gonou" the criminal to "Cho Hakkai" the companion, allowing himself to form new bonds and strive for a future. Although his inner darkness and hatred for his demonic nature never fully disappear, he learns to control and live with it, fighting to protect his found family rather than simply seeking punishment for his past sins.

Hakkai possesses several notable abilities. He is a master of chi manipulation, which he uses for various effects. Offensively, he can fire powerful blasts of energy capable of disintegrating enemies. Defensively, he can create strong protective barriers. He is also the party's primary healer, using chi to accelerate the healing of others, though this process drains his own energy significantly and he cannot effectively heal himself. He is an extremely skilled hand-to-hand combatant, proficient in martial arts. As a transformed youkai, he wears three limiters on his ear to suppress his immense demonic power. If the limiters are removed, he assumes a more powerful and dangerous youkai form, gaining increased speed, strength, and the appearance of dark markings on his skin. However, releasing this power carries the risk of succumbing to a berserker state or losing control, which is why he rarely does so, and only when the situation is dire.