Five ordinary male students at Binan High School spend their days lounging in the clubroom of their so-called Earth Defense Club, a group that does nothing in particular, and living together in the Kurotama dormitory. The members include the enthusiastic Unzen, along with Sukayu, Unohana, Oshamanbe, and Aso. One morning while taking a bath, they notice a slimy creature moving in the tub and manage to catch it, discovering it is a talking Pallas's cat named Nuru. Nuru has traveled from the distant future with a serious mission: the Earth faces an impending threat of destruction. However, rather than taking direct action, Nuru explains that he has only come to warn them of the crisis, leaving it up to the five boys to decide whether they want to fight for the planet. Suspicious of what seems like an attempt to dodge responsibility, the group nevertheless agrees to take action when Unzen enthusiastically volunteers, declaring that doing so is more fashionable. Using feline science, Nuru grants the boys the power to transform into the Haikara Romantic Troupe. As they embrace their new roles, a mysterious trio known as the Bankara New Elite Squad schemes in the shadows, plotting to take over the Earth. The story unfolds in the Taisho era, a time described as filled with the scent of romance and compassion, with the Defense Club members living as ordinary students by day while battling against those who threaten the planet.