Nagi has ran away from the mansion, with Hayate leaving to find her. Meanwhile, Nagi is thinking if Hayate has started liking Hinagiku more than her. Nagi imagines Hayate with Hinagiku and gets angry as she continues her wild imagination, but then Ayumu appears. Nagi calls Ayumu a thieving hamster. Hayate and Maria are watching them from a tree above and Maria asks Hayate who Ayumu is, with him simply saying that she is just a friend. He wonders what they are talking about and Maria thinks that they are definitely taking about Hayate. Ayumu tells Nagi what they should have a match to settle things. They have their match at a karaoke box with Nagi stating that she has only heard about a karaoke box but never been to one, commenting that it was smaller than her bathroom. Hayate wonders what Nagi and Ayumu are doing at a karaoke box, as he and Maria enter the next box to keep an eye on Nagi. Maria gets all excited about being in a karaoke studio and Hayate tells her that he wants to hear her sing. Meanwhile, Ayumu gets a score of 35 points for her singing. Nagi decides to sing a song, but it wasn't listed. The reason why Nagi could sing well is because she has been given voice training and singing practies from various famous teachers. Nagi gets a perfect score of 100 points, causing Ayumu to call Nagi her rival. The Sanzenin SPs pick up Nagi from the karaoke bar and Ayumu tells Nagi that they will have another battle with something else. Nagi replies saying that she will beat her in her own game again. Meanwhile, the butler and maid are still singing in the karaoke box.
After finishing singing, the karaoke monitor gives Nagi a score of 100% along with the quote: "wasn't that other person Gian". This is a reference to the character Gouda Takeshi (also known as Gian) from the series Doraemon, who loves singing but is very bad at it.