Alien invaders called Kiseichuu are plotting to gradually eradicate humanity by draining them of their H-energy, or libido, and undermining human reproduction. While this issue looms over society, Retto Enjo discovers that his childhood friend, Kirara Hoshino, has closed herself off from the world after a traumatic experience, and is worried about her. He speaks to her for the first time in many years, but their rocky relationship is unchanged. Retto is discouraged by this but encounters a Kiseichuu on the way home from school. He explodes with rage when he witnesses people being drained of their H-energy and losing their vitality, which causes him to…

Earth faces an unprecedented threat from an invasion by the mysterious Kiseichuu. The Kiseichuu feed on human sexual energy, also known as “H-energy,” and weaken the human population. High school student Retto Enjo is a member of the hero group HxEROS, who fight together to save the earth from the Kiseichuu.

Retto and others head to a nest of Kiseichuus to rescue Kirara who was abducted during a battle. Meanwhile, Kirara sets herself free from an enemy restraint and wanders alone in the nest. She comes across Chacha, a princess of Kiseichuus, who is considered different from the others due to her mutation and has been imprisoned. Chacha wants to stop her other comrades from destroying humanity and plans an escape with Kirara. Retto and others finally arrive at the nest and charge head-on, but…

The HxEROS headquarters generously grant Retto and the team a vacation at the beach, but when they arrive, they discover that the beach is covered with suspicious-looking sea cucumbers. Discouraged at the prospect of not being able to go swimming, the team head back to the hotel where they run into the Tokyo Branch, who have arrived to exterminate the sea cucumbers, and end up helping them in the extermination. Toma Taiga, the only male member of the Tokyo Branch, asks Retto to be his mentor. Toma says he admires Retto, but what secret is he hiding?

Due to the law passed by the new governor, Anno is arrested, and HxEROS is forced to disband temporarily. The Saitama Branch members have been working as heroes on their own, and they suspect that a Kiseichuu is masquerading as a human to take the position of governor. Chacha has the ability to tell whether or not a Kiseichuu has transformed itself, so she pretends to be a delivery person to investigate the identity of the governor. When Chacha rings the doorbell, the governor opens the door, but for some reason Chacha enters the residence. Retto and the team suspect that something is wrong and follow Chacha into the house, but they discover that…