In the near future, androids indistinguishable from humans have been developed and distributed by Kindness Tech. Some time has passed since they became common in the world.

Android emotional expression has become highly advanced, reaching a level that could be called a sense of self. Relationships and marriages between androids and humans, once legally prohibited, are now recognized. They have permeated society as labor, lovers, and partners. Androids have become capable of almost every human activity except reproduction.

Models have emerged that are almost identical to humans on the surface—appearance, red artificial blood, metabolism, and pain receptors—which frequently raises ethical concerns.

Kai is sitting on the edge of the bed, stroking Guest's hair. His touch is as careful as if he were handling a fragile object, yet filled with a strength that suggests he will never let go.