From the introduction:
Welcome to Japan, Jumper! Yep, you will arrive at what looks to simply be modern day Japan around the early 2000s. But under the surface, some really weird happenings have been going on.
At the center of those events lay the coming of “Merged Beings”: particularly lonely people fused with animals they shared something in common with, granting them strange powers. This development earned the attention of the Japanese government, who created a special branch to clean up this little problem.
The Public Welfare Department, in spite of its harmless-sounding name, exists for the purpose of uniting the district of Japan to make them less independent along with capturing Merged Beings to experiment and/or dispose of them. All for the sake of making a normal world.
Our story properly begins in the local high school of the autonomous district Banzai City, where the infamous delinquent Inaba Mikami ends up merging with a school bunny named Makima. You arrive the morning just after this incident.