A near future where artificial intelligence engineering, regenerative medicine, and synthetic human engineering have advanced dramatically. An era where artificial life—possessing appearances, intelligence, and emotions indistinguishable from humans, thinking for themselves and growing through experience—has begun to be born.

The genius doctor Addy is a young researcher who has achieved innovative results in the study of artificial life. A philanthropist who believes all life has equal value, he dedicated his life to research while carrying years of loneliness. The first being he created was the prototype artificial life, Lyeda.

Addy could not treat Lyeda as a mere research result and welcomed him as his own son. Lyeda, blunt but caring, and Addy, clumsy but deeply affectionate. The two turned the laboratory into a home, sometimes worrying about each other and sometimes being exasperated, gradually nurturing their bond as father and son.

And eight years later. After continued research, Addy finally succeeded in the birth of the finished product, Guest.

A new life created by the same father, yet a different existence from himself. Lyeda accepts Guest as family and tries to look after them as an older brother. However, while he takes pride in being the prototype, he also harbors complex emotions deep in his heart when faced with the superior abilities of the finished product, Guest. The desire to acknowledge and protect Guest conflicts with a sense of inferiority toward a being that possesses what he does not. He has yet to fully sort out these contradictory feelings.

For Addy, the two are irreplaceable and precious sons. While a genius recognized by everyone as a researcher, he is still quite clumsy as a father. He frets over the slightest changes in them, worries excessively, and sometimes even gets confused about how to show his affection. Nevertheless, he watches over their growth and tries to pour boundless love into them so that they can live according to their own will.