La Femme Mitsuki is the twenty-fifth episode of the first season of Kappa Mikey.
Gonard is preparing to use his "doom beam", a large mobile laser. Team LilyMu arrives in the battlewagon and confronts Gonard. Gonard raises a golden finger and turns the battlewagon, Lily's weapon, Mitsuki's shoes, and Guano's tail into gold. Suddenly Mikey arrives on the hoverjet. Gonard then turns the hoverjet into gold, but Mikey is able to jump off before it crashes. Mikey manages to dodge blasts from Gonard's golden finger and get close enough to grapple with him. In the struggle, Gonard's finger activates and shoots Gonard. Gonard is covered with a golden sheen, which itches him. Guano is crushed under the doom beam, causing him to end the scene.
The cast discover that the gold spray they are using has several itchy substances in it. Gonard runs off to go take a shower, telling Mikey that he will be unable to go to the movies with him later. Mitsuki asks if she can go to the movies with Mikey in Gonard's place. When Mikey finally acknowledges her, he asks her to go with him, which she agrees to.
Gonard is wandering through Tokyo in his underwear, still itchy. He comes across a guitar, which he uses to scratch his back. The guitar's owner is impressed by Gonard's "music" and heals Gonard's itching with an ointment. He introduces himself to Gonard as Harmony Sunshine.
Mikey and Mitsuki are outside the movie theater, discussing the movie they just saw. While Mikey runs back inside to get popcorn, Mitsuki is engaged in conversation by someone in a nearby mailbox. The mysterious person claims to recognize Mitsuki as "Agent M" and alludes that he knew her in the past. Mitsuki denies knowing him before knocking over the mailbox and fleeing.
Gonard, still in a state of undress, approaches Lily and tells her about his new friend. Gonard wonders if he should become an "earthie", like Harmony Sunshine. Lily encourages him to do so, thinking that he will embarrass himself.
Mikey catches up with Mitsuki, who attempts to hurry Mikey back home. She is once again confronted by the mysterious man in the mailbox, but manages to distract Mikey. Mitsuki tells the man, whom she refers to as "Agent F", that she has no business with him. Agent F reveals that Mitsuki was once a spy. Mitsuki insists that her days as a spy are behind her. F attempts to convince her to return to her old life, but she refuses and flees once again. Mitsuki returns to LilyMu Towers, but is followed by Agent F. He gives her a small, porcelin dog.
Mitsuki is in her bedroom. She presses a hidden button on her wardrobe, which pulls back her wall and reveals a deep red wig, which Mitsuki puts on. She thinks on Agent F's plea for her to return to being a spy.
In a flashback, Mitsuki's former life as a spy is shown. She and Agent F infiltrate a heavily-guarded compound to retrieve film containing damaging photographs. The film is hidden inside a small, porcelain dog, the same one F would give Mitsuki later.
Ozu approaches Guano at the studio and asks what happened to the last week's footage. Guano tells him that Mikey destroyed it. They contemplate holding Mikey responsible for his actions, but laugh off the idea. Gonard arrives, now in his "earthie" persona. Guano questions Gonard's new behavior, and Gonard reveals that Lily had suggested it to him.
Mikey approaches Mitsuki in her bedroom and asks her to go with him to a dog show. Mitsuki accepts, casting aside her thoughts of returning to her old life.
Guano calls Lily to the studio, where Gonard and Harmony Sunshine are meditating. Guano chastises Lily for telling Gonard to become an "earthie", but Lily defends her actions. Gonard then tells Lily that Harmony will be staying at her apartment for several days. Lily angrily refuses, prompting Gonard and Harmony to try to turn her into an "earthie".
Mikey kidnaps Guano, planning to enter him in the dog show. Mitsuki is contacted by Agent F again and tells him that she has chosen not to go back to her old life. Agent F refuses to accept her decision and threatens to go after Mikey in order to convince her to return.
Mikey takes Guano to the dog show, dodging several attacks, partially thanks to Mitsuki. Mikey eventually notices Mitsuki subduing the attacks and confronts her about them. Mitsuki reluctantly tells Mikey about her past life.
Gonard and Harmony have taken up residence in Lily's apartment, where they annoy her with their antics. Lily becomes fed up and revokes her suggestion that Gonard be an "earthie". Gonard refuses to go back to his old ways, however.
Mikey is impressed by Mitsuki's former identity. They are attacked by spies again, but Mitsuki manages to fight them off. Mitsuki then realizes that the dog that Agent F had given her has a tracking device in it, and destroys it. Mikey suggests a plan to deal with the spies.
Lily calls in Ozu to help her deal with Gonard. Ozu gives him and Harmony a long lecture about proper behavior, eventually turning them into normal, productive members of society.
Agent F goes to LilyMu Towers to find Mikey and Mitsuki. He and his agents break into Mitsuki's apartment, but discover that they are not there. Mikey and Mitsuki contact them via the television from their headquarters. The threaten to release information about the agency to the public unless the spies agree to stop harassing them. They agree, with Mitsuki being forced to incapacitate Mikey to keep him quiet.
Mikey awakens in his apartment with Mitsuki nearby. She tells him that Mikey had fallen ill before the movie and that they had never gone, which Mikey believes. She tells Mikey about the dog show and he agrees to go with her.
The LilyMu episode is finished, with Gonard accidentally turning the controls of his doom beam into gold, disabling it.
- This episode's title references the phrase "femme fatale".
- This episode references the novel Goldfinger and its film adaptation.
- Harmony Sunshine is portrayed as a stereotypical "hippie".
- Agent F references the television series Get Smart.
- Gonard references the book The Cat in the Hat.
- Gonard references the song "I Am the Walrus".