In 2008, the Japanese government began hunting people who identify as otaku in an effort to protect the country's culture. In just one week, the enforcement agency known as the SSC captured almost every otaku by force and confiscated their memorabilia. One passionate man calling himself Otaku Hero refuses to allow this agency to do as they please: he raises a resistance army made up of other displaced geeks who band together to help defend their culture. Three years later, the fires of rebellion wane as all hope seems lost for otakus. Spurred on by his ally—the magical girl Anarchy—Otaku Hero commands the resistance in an effort to reunite Anarchy with the other two other magical girls: Blue and Pink. By combining the power of this trio, the resistance may be able to defeat the SSC and save otaku culture for everyone.

Taking place after the events that occurred in Hayate no Gotoku! Can't Take My Eyes off You. Hayate, Nagi and Maria return to their daily lives at the Sanzenin Mansion and the Violet Mansion. (Source: Hayate no Gotoku! Wikia)

In the seaside village of Hinashi Town, Kai Ashimoto's grandfather is one of the locals who reinforces the legend that mermaids lurk near Merfolk Island and consume humans. Due to allegedly attracting merfolk and subsequently causing the death of the elder's mother, music is seldom discussed in the Ashimoto household. Even so, Kai finds solace in making looped beats on his laptop and uploading them to the internet. Despite his reserved and glum demeanor, Kai is approached by Kunio and Yuuho Ebina, two cheerful classmates that happened upon one of his videos. The pair ask him to join their rock band but are met with apathy. Nevertheless, Kai agrees to accompany them in a practice session on Merfolk Island, where he soon witnesses something that he cannot explain. Later that night, Kai is composing music in his room when he attracts a familiar entity—a mermaid. As she twirls and grins to the sound of his stereo, Kai discovers a number of aspects about the being who introduces herself as Lu: she possesses incredible water manipulation powers; she buds a pair of functioning legs with the sound of music; but most notably, she is a truly benevolent creature who simply wants people to like her. Fostering a dynamic friendship, Kai and Lu gradually come to express their genuine selves, testing the long-standing boundaries that have deafened the resounding harmony among the people of Hinashi Town.

Prequel film of UN-GO telling the encounter of Shinjuurou and Inga.