Several years have passed since Binan High's Earth Defense Club saved the world from an alien invasion that sought to sap the world of love—okay, maybe that's how it happened. The truth is that no one really remembers if something like that happened or not, and now five friends-of-convenience share the defunct Earth Defense clubroom to goof off after school.
But even if they don't know the club's history, their gathering at the local bathhouse attracts the attention of another adorable extraterrestrial: Karurusu, the otter-prince of Honyaraland. As part of his planet's conquest initiative—"tributary outreach program"—Karurusu transforms these five misfits into magic knights who will bring happiness to all lost souls.
Unfortunately, the fox-prince Rafunui has his own ideas about how to improve this Earth colony, empowering his own trio of dark knights to oppose this new batch of magical boys.