While looking for a better vantage point for viewing the monster attacking Tokyo, Silk, Vivienne, and Tsubomi get crushed by the giant hero UFO-Man as he comes to save the day. He resurrects them, but at the cost of being unable to fight the monsters himself. He gives Silk the power to transform into a giant heroine, but her costume only lasts a few short minutes before beginning to disappear. Silk saves the day by defeating her first monster.

Vivienne and Tsubomi learn that they, too, can transform into giant heroes, but with the same caveat as before. Tsubomi transforms and tries to fight the monster, but is quickly defeated. Vivienne transforms ad fights the alien, and Tsubomi's brother is captured by the attacking alien.

The girls learn that their power comes from being embarrassed (because their costumes keep gradually disappearing until they are naked), and the more embarrassed they become, the stronger they become. Vivienne immobilizes the alien, but it breaks free. The girls learn that the core of the alien must be destroyed. Silk transforms and defeats the alien. Silk thinks Vivienne is mad at her and also has a crush on Makoto, Tsubomi's older brother.

The local TV station has put out a reward for pictures identifying the Ultimate Girls. When the next monster attacks, Tsubomi goes to fight it, but appears to be defeated after posing for all the photographers. As her costume begins disappearing, she begins to act sick, thus tricking the monster into coming to help her. She then rips out its core and defeats it.

Silk and Vivienne are tricked into working with Tsubomi at her part time job: waitressing at a cosplay cafe while dressed (respectively) as Hazuki from Moon Phase and Sailor Moon from Pretty Soldier Sailor Moon. While Tsubomi is entertaining the customers, Silk and Vivienne go on break just as a new monster appears. Vivienne has trouble beating the monster until she sees Silk cheering her on. After the fight, Makoto tells Silk that he likes the Ultimate Girl who just won the battle, which causes Silk to become upset and run away.

The girls go to the beach, unaware that Silk's sister has set up an event there she is hoping to use to discover the true identities of the Ultimate Girls. Silk continues to misunderstand Vivienne's feelings for Makoto, and Makoto is hoping to snap a picture of an Ultimate Girl as she changes back to normal. After Silk defeats the monster, Vivienne explains that she's not in love with makoto, but that she has someone else.

Silk's class goes on a school trip, and she leave UFO-man behind in her room. On the way past Mount Fuji, a monster appears and puts everyone to sleep. UFO-man arrives and wakes up the girls. Silk fights the monster, but begins to lose when the monster begins tickling her. However, this also increases her power, and she defeats the monster, but not before everyone wakes up and the bus with her classmates drives away before she finishes the fight. As she's walking down the highway after the fight, Makoto stops and picks her up, giving her a ride to where the bus was going.

The girls and their class arrive in Kyoto and enjoy an evening relaxing in an onsen after spending several hours learning Zen meditation. Vivienne takes the other girls out for a night on the town in order to cheer up Silk, who has learned that Makoto is going back to Tokyo early. A new monster appears and Tsubomi appears to defeat it after using her meditation techniques to lure it into an unguarded state. However, the monster was not defeated, and it escaped.

The girls are still in Kyoto the morning after the monster escaped. Vivienne arranges for Silk and Makoto to be alone at an amusement park while she and Tsubomi go off somewhere else. While they are going around, Makoto confesses he likes "Little Boobs" the best of the three Ultimate Girls, which causes Silk to become very embarrassed. At that moment, the monster reappears within the amusement park. Even though she's feeling sick from riding a rollercoaster three times in a row, Vivienne fights and defeats the monster in order to allow Silk to continue her "date".

It's Christmas time. After giving a present to Makoto at a party, Silk finds out he's going to the United States to study journalism. In order to try to cheer her up, Vivienne and Tsubomi take her to Comike, where Silk promptly gets separated from the other two girls just as a new monster appears. After defeating the monster, Silk admits to Makoto that she's one of the Ultimate Girls.

Makoto misunderstands Silk's confession, thinking she is only cosplaying, and he asks if he can tak her picture when she's in costume. Tsubomi takes the opportunity to get the other girls to cosplay with her as the Ultimate Girls. Makoto finds out that Okamura is a dōjinshi collector who has collected a very large number of Ultimate Girl books and has a table reserved for the final day of Comike to sell a book of his own. Makoto is inspired by him and decided to become the ultimate Ultimate Girls collector. Suddenly, a new monster appears and defeats Tsubomi in one punch, but not before she notices that her brother, Makoto, is the core of the monster. Vivienne goes to fight the monster, but starts losing to it, too. Tsubomi tells Silk that the monster is her brother.

Vivienne is defeated, with the monster demanding to know who they really are. UFO-man explains how the monsters come into existence and states that there isn't a way to save Makoto as he is directly connected to the core of the monster. Silk offers to give up her body so that Makoto can live once the monster is defeated, and asks UFO-man to erase any memory of her from Makoto. She then goes to fight the monster, which she defeats after destroying its core. However, she hesitated before destroying it, and didn't hurt Makoto very much, so UFO-man used his power to repair Makoto instead. Makoto decides to not go to America after all, and gives her a picture he took of her while she was transformed.