Joker: One Operation Joker Vol 1

Written by Satoshi Miyagawa (Uchuu Senkan Tiramisù) and illustrated by Keisuke Gotou, this manga finds Batman transformed into a baby following an accidental fall into the same vat of chemicals that turned the Joker into his evil self.

Immediately after accident, the Joker finds himself lost without his arch-nemesis and takes it upon himself to raise baby Bruce Wayne. However, the Joker finds fatherhood to be a lot more difficult than he initially thought.