The upper half of a chu-u appeared as an aged human, either male or female. The bottom half of a chu-u was in a misty cloud of roughly 5 feet (1.5 meters) in width. Its skin was green and wrinkled, and they had narrow eyes. They often appeared wearing clothing, usually red, and with a crown of thorns.
Upon meeting another humanoid, a chu-u began telling the story of its life. This tale described its former life and how it became a chu-u. They pleaded with humanoids to accompany them to the River of Three Routes, so they could testify on their behalf to the dreaded King Judge, who sentenced and delivered punishment to spirits. Afterwards, they were returned to the Material Plane. Since the King Judge would often spend a lengthy time deliberating on the chu-u's fate, often up to 100 years, the traveler rarely, if ever, learned the outcome of their intervention.
If they refused to aid the chu-u, the spirit became enraged and swore vengeance. It then transformed into a mist and was drawn into the ground. The vengeance of a chu-u occurred when the victim least expected it, often several years later. The chu-u transformed its arm into misty tendrils, which could be lengthened an unlimited distance, and choked their victims. This attack could be repelled by a dispel magic spell. Someone who had been cursed by a chu-u was able to have the curse lifted by visiting a shugenja, who performed a purification ritual.
Chu-u spent their time stuck along the shores of the River of Three Routes, unable to fully enter the Spirit World. On the Prime Material plane, they remained underground until they encountered a humanoid.