Mai is a woman whose fiancé, Youji, dies in a mountain climbing accident. Driven to have his child, she approaches the genetic research facility where he worked, a place with the technology to create a clone from DNA. She cannot afford the procedure.

To fund the project, Mai accepts a distinct and demanding job from the facility: becoming a DNA Hunter. The role involves procuring semen samples from specific, often hard-to-reach men for clients who want children by those individuals, using any means necessary.

Before joining the team, Mai must pass a qualification test by selecting a random stranger and successfully obtaining his sample. This presents a profound moral test of her resolve to achieve her goal.

After passing, Mai officially becomes a DNA Hunter. Her first major mission is to collect a sample from a very wealthy man who is deceitful, corrupt, and views women only as sex toys, a task complicated by his nature.

Mai and the team eventually meet their ultimate confrontation with an underground mafia organization attempting to steal their secrets, the final obstacle in her journey.