Humans ; : :The human protagonist. A girl that has a gentle personality and cannot resist to help someone in need. She is currently on second grade of middle school. She has a long, straight purple hair. She is good at cooking and sewing, but her naming sense is bad. She is good friends with Ara (), Eimi (), and Mii (). ; :Yuka's mother. She is strict with her daughter's grades due to Yuka failing her middle school entrance exam at one time. ; : :Yuka's male classmate who is good at
claw crane games. He is one of the first human after Yuka who knows the existence of underground-dwellers. He has confessed to Yuka once, but hasn't got the answer from her yet. ; :Yamato's younger sister. After she met Chi-chan, she wants to play and become friends with him. ; :Yuka's childhood friend who is older than her. When he and Yuka was in elementary school, he used to play pranks on Yuka, which made her angry. He did this because he had a crush on Yuka, and wanted her attention.
Underground-dwellers ; : :The dweller protagonist. An underground-dweller that had stuck on the hole he came from when he wanted to return home. His body is about a size of a crane game prize, and he has a round, yellow body. At first, he was afraid of humans because he thought that if he gets caught, he would be dissected by them. But then, since his meeting with Yuka, his judgement of humans changed. :Since the names of underground-dwellers are usually unintelligible to humans, he gets the name "Chi-chan" from Yuka, from the term , the Japanese word for underground-dweller. He has a verbal tic of when ending his sentences. ; : :Chi-chan's friend. He came to the human world searching for Chi-chan that went missing from the underground. He has a round, green-colored body. He gets the name "Joe" from Yuka due to his verbal tic, . ; :An underground dweller who respects Chi-chan. ; :Chi-chan's father who appeared in Episode 12. He wears a silk hat and has a mustache. He has a yellow body like his son. ; :Chi-chan's mother who appeared in Episode 12. She wears an apron and a skirt. She has a yellow body like her son.
Aliens ; : :An alien girl who was rescued by Yuka when her spaceship crash landed to Earth and Yuka was climbing at the time. The name "Ucchan" comes from , the Japanese word for alien. She can create various gadgets. ==Media==