Once you get your own hanko, it is very important that you handle it with caution and keep it in a safe place. Unlike signatures (which is hard to forge), anyone can easily use your hanko, and it is indistinguishable who actually used the hanko. If somebody else uses your hanko on any contract sheet, it is estimated that YOU have agreed the contract, and you will have to take responsibility about the contract.
So, you should not easily put your hanko into someone’s hands.
If you are involved in a legal trouble related to using hanko, be sure to consult an attorney as soon as possible.