On physical examination day, many of the girls are feeling stress about their weight, measurements and fitness. Nozumu distracts them by deciding to judge the "social worth" of students so that they will know whether they are living "above their station." Kitsu seizes on this idea, scolding everyone who possesses any luxuries, appalling Nozumu to the point where he decides to go on a hedonistic binge before killing himself. In the second half he encounters some of his students at a hot spring and is frightened to learn the spring has the power to remove their "toxicity" giving them well-adjusted personalities.

Nozomu notices a few members of the class playing a "spot the differences" game. Nozomu tells them that it is important to spot mistakes and he instructs the class in how life is filled with mistakes. He asks the class to identify mistakes in their lives after pointing out several of his own. After Nozomu contradicts himself, saying that a mistake was the correct action, Kafuka reasons that if a mistake comes to light, it is correct, resulting in many people approaching her, confessing their mistakes, making them correct. In the end of the first part, a boy approaches Nozomu, calling him "Dad." The second part of the episode reveals that he is actually Nozomu's brother's child, Majiru. Nozomu asks him to prove that he is indeed his nephew, and then asks all of his students to prove that they are the real one. When Majiru asks Nozomu to prove he is genuine, Nozomu is unable to come up with a response, and runs off. The episode ends with a sequence that deals with Majiru's hair fetish.

Nozomu Itoshiki and his students enjoy the festival of Tanabata and talk about instances where people pay more attention to the trivial details of many objects rather than the main subjects. In the middle of their conversation, which Ikkyū-san later joins, the alien race El Niño suddenly invades Japan with their mecha army. Fortunately, Chiri digs up an ancient mask and activates its hidden power to defeat the alien force. The aliens admits their mistake of paying attention to trivial aspects of Nozomu's students rather than the progress of their invasion. At the end, Nozomu and Ikkyū-san do not remember how Japan was saved from the alien invasion, as they were paying attention to trivial details of the battle scene. In the second part of the episode, Jun Kudō is reading books in the school library, while Nozumu is worried about Jun's desire to read everything in the world, which could eventually include Nozomu's own embarrassing mind. When Nozomu's other students visit the school library, Jun tells heart-warming stories that move every one of them to tears. Nozomu feels even more certain of Jun's ability to read people's minds, so he puts himself in a freezing room full of penguins to prevent Jun from reading the conclusion of the episode. The third part of the episode shows what happened between Nozomu's nephew, Majiru Itoshiki, and Kiri Komori while the alien invasion of the 'A Painter by the Roadside' episode was undergoing outside the house.

A special summary episode of the second season of Sayonara Zetsubou Sensei, focusing on the girls that were not introduced in the first Zetsubou Shoujo Senshuu: Otonashi Meru, Fujiyoshi Harumi, Kaga Ai and Mitama Mayo.