Chimoguri Ringo to Kingyobachi Otoko

A terrifying entity has been terrorizing the local community: a monstrous man whose head is a glass fishbowl. When he attacks, the goldfish inside leaps out to drain the victim's blood, irreversibly transforming them into a goldfish. High school student Kousuke suffers this nightmare firsthand when his younger sister falls prey to the creature. Left with no alternative, he does his best to care for her in her new aquatic form, struggling to cope with the bizarre tragedy that has upended his life. Everything changes when Kousuke encounters Ringo, an eccentric girl clad in a school swimsuit who carries an umbrella and wears a firearm around her neck. She is an apprentice "blood diver," using the gun to propel herself directly into the wounds of the fishbowl man's victims. If she arrives in time, she can halt the transformation process entirely. Ringo's mentor, Ichigo, reveals that a method may exist to reverse the curse and restore those already turned back into humans. Fueled by hope, Kousuke resolves to assist Ringo in uncovering this cure, determined to save his sister and the afflicted loved ones of his classmates from their grim, watery fate.