"Rabbit Killer" is one of the Quests found in OMORI.
It's a side quest, meaning that its completion is not mandatory.
Leafie has a burning hatred against bunnies and wants you to kill as many as possible.
To finish this quest you have to kill 50 bunnies.
Going to 100 will grant you the "Bunny Exterminator" Achievement.
Leafie rewards you one item at the respective Milestones:
5 Bunny, 25 Bunnies and 50 Bunnies.
Cotton ball, Bunny ears and Rabbit foot.
List of Bunnies that count towards this quest:
- Rabbit?s do not count towards the kill count, despite the fact that they are also bunnies. This is probably a humorous nod to the Rabbit?s Foe Facts journal entry, wherein Omori and Aubrey decry it as "an abomination" as opposed to any sort of rabbit or bunny.