Manic Monday is the twelfth episode of the second season of Kappa Mikey and the thirty-eighth episode overall.
A giant, wounded Gonard is trampling through the streets of Tokyo, with Lily and Mitsuki hanging onto his hair. Mikey and Guano confront Gonard, and mention that Gonard's injuries are due to a previous battle. Mikey engages Gonard, causing Lily to fall from his shoulder. Mikey manages to swoop in and save Lily from her fall. Gonard loses his balance and falls backward, causing Mitsuki to fall as well. Mikey is oblivious to this, and Mitsuki falls to the ground. Guano ends the scene.
Mikey explains to Mitsuki that his preoccupation with Lily is due to him watching "Lily Week" on television. Ozu arrives and asks Guano and Gonard to help with spring cleaning. While cleaning, Guano discovers a tiki idol, which he and Gonard take a liking to. Ozu, however, demands that they throw it away.
Lily is at the mall signing autographs for her fans, including Mikey. Mitsuki approaches her and complains about the disparity in affection Mikey has for the two of them. Lily, however, is annoyed by the attention she is getting from her fans.
Lily attempts to disguise herself to avoid her fans. She and Mitsuki and approached by an old man who sells them a pair of friendship bracelets.
Guano and Gonard have finished the cleaning. They both attempt to stealthily retrieve the tiki from the garbage, but discover each other. The two fight over the tiki, but eventually agree to share it.
Lily and Mitsuki are back in their apartment, where Lily is still being pursued by paparazzi. Lily and Mitsuki express how they each believe the other to have a more desirable life. When the two of them loudly proclaim that they each wish that they had the other's life, the friendship bracelets they are wearing activate and cause them to swap bodies, shocking them. They realize that the bracelets were responsible for the swap. Mikey arrives, giving Lily the idea to use their situation to avoid him. Mitsuki is reluctant at first, until she realizes that she will get to spend more time with Mikey.
Mitsuki, in Lily's body, goes to spend time with Mikey. Lily, in Mitsuki's body, is relaxing at home without her fans bothering her. She is interrupted by Mitsuki's charity activist friends, who insist that she come and help as Mitsuki normally does; Lily reluctantly agrees.
Gonard and Guano are at LilyMu Studio with the tiki. A series of unfortunate accidents occur around the tiki. Ozu discovers the tiki and informs them that it is cursed and brings bad luck to those around it. Guano and Gonard are dismissive of Ozu's warning, but are forced to take the tiki home after Ozu demands not to see it. Guano runs off with it before they can decide who will get it.
Lily is out picking up litter with Mitsuki's friends, but they question why she is so reluctant to do so as Mitsuki typically enjoys it.
Mitsuki is out having lunch with Mikey, where she manages to impersonate Lily.
Lily is feeding a group of poor children with the activists. The activists then give away prized possessions to the children. Lily struggles to find something that she can bear to part with, with one of the activists eventually forcing her to give away the contents of her purse. Lily loses patience with the activists. She then discovers that Mikey and "Lily" have become a famous power couple, angering her.
Guano arrives at Gonard's apartment, severely anxious. Guano demands that Gonard take the tiki off his hands, to which Gonard agrees. Later, the tiki causes Gonard to be mauled by a snake.
Lily confronts Mitsuki, complaining that Mitsuki is ruining her image by dating Mikey. Lily demands that they switch back to their own bodies, but Mitsuki cannot bring herself to do so as it would mean losing Mikey. Lily angrily approaches Mikey and asks him out, with her aggressive demeanor infatuating him. Mitsuki agrees to switch back, but the two discover that they cannot do so and that the bracelets have become stuck to their arms.
Lily and Mitsuki angrily confront the old man who gave them the bracelets. He informs them that the bracelets will come off when Lily and Mitsuki learn what they each have that the other lacks. The two of them resolve to help each other undo the spell. Just then, Lily is kidnapped by the activists. Mitsuki calls Mikey for help.
Gonard's apartment has been trashed, presumably due to the tiki. Gonard anxiously calls Guano to come help him.
The activists interrogate "Mitsuki" to find out why she has had such a change of heart regarding their charity activities. They attempt to brainwash her to return her to her old ways.
Mikey and Mitsuki rush to rescue Lily. Mikey reveals that he has begun to fall for "Mitsuki", due to Lily's assertive personality. Mitsuki realizes that Lily's assertiveness is what Lily possesses that she does not.
Gonard and Guano throw the tiki off of a rooftop to dispose of it. Afterward, Ozu confronts them and asks why the tiki is in LilyMu Studio. The two of them are confused, as to why their attempt to dispose of the tiki did not succeed. Ozu informs them that the curse of the tiki must be passed on to someone else. They take it to the Tatami Megastore, where Mr. Tatami's children take it off their hands. The tiki, however, grants the boys good luck instead of bad luck.
Mikey and Mitsuki arrive at the recycling plant where the activists are holding Lily. They manage to free Lily and Mitsuki angrily berates the activists for their treatment of her. Lily agrees to go on a date with Mikey, for Mitsuki's sake. Lily realizes that Mitsuki's selflessness is what Mitsuki possesses that she does not. The two of them realize that they have rubbed off on each other. The bracelets activate again and switch the two girls' bodies back. Mitsuki reconciles with the activists.
The LilyMu episode is finished, this time with Mikey rescuing both Lily and Mitsuki.
- This episode's title and premise are a reference to the novel Freaky Friday and its adaptations.