Cho Hakkai, originally named Cho Gonou, was born human and orphaned, raised by Catholic nuns. He grew up as a quiet and withdrawn child who rejected faith. As an adult, he worked as a schoolteacher and fell in love with a woman named Kanan, later discovering she was his long-lost twin sister. They lived together as lovers despite the taboo.

Villagers kidnapped Kanan and offered her to the youkai lord Hyakugan Maoh. Discovering her absence, Gonou massacred half the village, slew Hyakugan Maoh, and slaughtered nearly all youkai in the castle. He found Kanan imprisoned; she revealed her pregnancy with Hyakugan Maoh's child and took her own life using Gonou's knife. Chin Yisou, Hyakugan Maoh's son and the massacre's sole survivor, attacked Gonou, inflicting a near-fatal wound. Yisou then dripped his own blood onto Gonou—making himself the thousandth youkai Gonou had encountered—triggering Gonou's transformation into a youkai, fueled by Yisou's taunts about the incest and Kanan's death.

Declared dead as Cho Gonou, he was renamed Cho Hakkai by the Three Aspects, who granted him a second life. The name "Hakkai" references Buddhism's Noble Eightfold Path, forbidding intoxication and killing—a penance aligning with his inability to get drunk and resistance to certain drugs. He harbors deep self-hatred for his past actions and youkai nature.

Hakkai joined the Sanzo party as the driver, healer, and caretaker. He wears three silver magitech limiters on his left ear to suppress his youkai form and maintain a human appearance. Physically, he is tall and lanky with messy brown hair, green eyes, and a large abdominal scar typically hidden by clothing. His right eye is a magitech prosthetic, requiring glasses for clear vision. Without the limiters, his youkai form emerges: pointed ears, claws, a slitted yellow left eye, and black vine-like tattoos swirling across his skin. This form grants enhanced strength, speed, and agility, along with the ability to manipulate his vine markings to ensnare targets or conduct energy. However, removing the limiters risks loss of sanity, especially under the "minus wave," making him uncontrollably violent.

His personality presents as mild-mannered, polite, and perpetually smiling, masking profound inner rage and melancholy stemming from guilt over his human-era killings. He exhibits a vengeful side when provoked, particularly if companions are threatened. Despite his calm exterior, he possesses a cutting wit and excels at reading people. He is deeply loyal to the Sanzo party, serving as a stabilizing force. His relationships are complex: he shares a marriage-like bond with Sha Gojyo, regards Genjo Sanzo with unwavering faith, and acts as a gentle mentor to Son Goku—though Goku sometimes helps Hakkai regain his humanity during rages.

Hakkai's abilities center on kikou jutsu (chi manipulation), generating energy blasts, defensive barriers, and minor healing. He is skilled in hand-to-hand combat. In critical battles—such as confronting a berserk Seiten Taisei (Son Goku's unleashed form)—he removes his limiters to amplify his powers, once using his vine markings to bind Goku and channel lightning through them, nearly dying.

In a previous incarnation, Hakkai was Tenpou Gensui, a Western Army field marshal in heaven. Though less meticulous than Hakkai, Tenpou shared traits like intellectual curiosity, a dry wit, protectiveness over loved ones, and a latent violent streak. Both identities reflect violence emerging when those close to him are endangered.

Hakkai shows gradual acceptance of his youkai nature, influenced by Gojyo and the party. He defends other youkai but never seeks forgiveness for his past, remaining uncomfortable with his transformed state. His journey is marked by ongoing penance, balancing his nurturing role with the ever-present risk of his destructive potential.