Chimoguri Ringo to Kingyobachi Otoko

A man with a fishbowl for a head attacks people, causing his goldfish to leap out and drink their blood, transforming them into goldfish. High-schooler Kousuke’s little sister becomes a victim, and he must care for her in this new form. He meets Ringo, a girl in a school swimsuit who carries an umbrella and a gun. Ringo is an apprentice blood diver who uses the gun to enter wounds of those attacked, preventing their transformation if she acts quickly. Her mentor, Ichigo, mentions a possible way to reverse the transformation. Kousuke decides to help Ringo find a solution to restore his sister and others from his school who have also been turned into goldfish. The manga was originally published in a cancelled magazine but continued in Comic Earth Star. One-shots included in later volumes are "Jigoku," "Kappa's Dinner Table," and "Oni Killer."