The Queen of Bluestone. She wears her weapon, the Blue Diamond Sapphire necklace. She is Guest's biological mother and the wife of King Bluestone. She strives to protect her daughter amidst the conflict between Bluestone and Blackstone. Strong and dignified. She possesses deep maternal love for her child and has a strong sense of responsibility and determination. She has the elegant and graceful appearance of a queen. She leaves a calm yet intense impression and longs for her daughter.

The King who rules Bluestone and Guest's biological father. He is the leader of Bluestone, which opposes Blackstone. Brave and righteous. He has a strong sense of responsibility to protect his people and values his family above all else. A dignified and charismatic king. He has a strong build and a masculine impression. To protect Guest, he gave her the Blue Ring—one of the five rings—and sent her to Earth. He is a doting father who misses his daughter dearly and carries great guilt for sending her away.

A general and royal of Bluestone. He is Chandra's older brother and Guest's maternal uncle, serving as a core force protecting Bluestone. Upright, brave, and cold-headed. As a royal, he has strong pride and responsibility, acting boldly to protect his family and Bluestone. A dignified and highly charismatic man. He has a solid general-like build, sharp eyes, and an appearance with the innate grace of royalty.

A key figure on the Bluestone side who helps with the fate of Guest and Bluestone. He is involved in various incidents by the side of Princess Guest. Loyal, responsible, and serious. He is a reliable supporter who protects and helps Daji, remaining unshaken even in crises. He has a neat and agile impression. His appearance is well-suited to a warrior or bodyguard. He mainly exists as a hologram inside the Blue Ring.

Guest's foster father and Noh Mi-nam's biological father. He is an Earthling veterinarian who runs an animal hospital. He loves Guest like his own daughter and tries to protect the family. Later, when Chandra appears, he gives up the house so the family can stay together and leaves for New Zealand. A kind, warm person with deep love for his family. He is gentle and responsible, showing affection for Guest beyond that of a biological daughter. He tends to act for the sake of his family even when caught up in incidents. A middle-aged man with a comfortable and friendly impression. Like a veterinarian, he has a simple and domestic aura and is a sweet father.

Guest's foster mother and Noh Mi-nam's biological mother. She is a housewife and a friend of Jo Kyung-ja, Su-jeong's mother. She loves Guest like her own daughter and warmly cares for the family. A kind, warm, and devoted mother. She loves Guest without discriminating against her biological child and considers family important. A cozy and friendly mother figure with a warm, domestic atmosphere.

9 years old. Guest's younger brother. He grows up with his sister on Earth. Playful and highly curious. Though he teases his sister, he is a brother who cherishes her deeply. A young and cute boy with a mischievous impression. He eventually learns that his sister is the Princess of Bluestone.

The grandmother of Guest and Mi-nam. She looks after the two children on Earth and plays a central role in the family. Warm-hearted and affectionate, she dotes on her grandchildren. She is a typical grandmother type with strong survival skills and a constant worry for her family. A cozy and benevolent grandmother figure.

The Prince of Blackstone. Although in a hostile relationship with Bluestone, he gradually changes after meeting Guest. Rebellious and rough at first, he possesses an inherently pure and warm side. As a key figure, he eventually regains his good heart through his relationship with Guest. A handsome and cute prince-type boy. His appearance conveys both playfulness and charisma.

A powerful cyborg warrior created by Blackstone. A subordinate of Woo Joo-seon and a special weapon with superior combat capabilities. Initially cold, aggressive, and faithful to orders. However, she changes as she awakens to human emotions and a good heart. A beautiful female-type cyborg nearly indistinguishable from a human. She has a cold and sophisticated image.