After her boyfriend Shinpei says he'd be willing to get married if a third person is involved, a flustered Mia takes him to meet her ex, Takuzo.

Takuzo realises Mia is only using him to get Shinpei to marry her. After a chat with his coworker, he decides to attend a matchmaking party.

Shinpei takes Takuzo up on his suggestion of a hot spring and invites Mia along. During a stop en route, Takuzo runs into his ex-girlfriend.

Mia struggles to suppress her sexual urges. When Takuzo gets an urgent call from work, he entrusts Mia and Shinpei with his share of the chores.

After Mia realises that Takuzo and Shinpei feel jealous about each other's closeness with her, she hopes they can figure out how to get along.

Mia grows unsettled by Takuzo and Shinpei's newfound closeness. When the guy's go fishing together, Mia's friend hints that they might become intimate.

Mia leaves the house after seeing Shinpei and Takuzo in bed together. As Shinpei worries about her, Takuzo questions Shinpei's feelings towards him.

Takuzo's mother, Natsuko, visits and is shocked to learn about her son's situation. Later, Mia decides to tell her own mother the truth.

Takuzo agrees to a one-week trial cohabitation with Tenma. However, Mia and Shinpei worry that he won't come back to them.

Mia realises she has underestimated the legalities of having children in a three-person marriage. Shinpei's brother makes him a surprising offer.