Kei-In is a Hanko to be stamped on a contract consist of more than 2 pages. You don’t need to stamp Kei-In in the case that a contract has just one page but in the case that the one has more than 2 pages, you need to stamp Kei-In in order to confirm that one contract is consist of whole pages of documents. Showing Kei-in is stamped on whole pages has effect to prevent insistence that pages are added or a contract is altered
Kei-In has two cases of stamping
1st case is to stamp on a backside of the boundary between the last page of contract and a binding paper which binds up whole pages of contract.
2nd case is to stamp on the boundary between pages.