If I start a business while employed, will my employer find out through labor and health insurance that I am a responsible person?

The short answer: you will not be discovered through labor or health insurance.

• After becoming a responsible person, your labor and health insurance can remain with your current employer; you do not need to move it to your new company.
• Your labor insurance, health insurance and pension rights at your current employer are unaffected, and no documents from the new company are sent there.
• The one thing to watch is employment insurance benefits (such as parental leave allowance): you cannot hold responsible-person status while applying for them.

However, the responsible person's name is public government data. If your employment contract explicitly prohibits serving as the responsible person of another company, HR could still work it out by searching your name together with the registered address. In that case it is safer to have a relative or friend serve as the responsible person (for a limited company the responsible person must hold a capital contribution; for a company limited by shares this is not required).

One situation to distinguish: if you are currently insured through a district office or an occupational union, or as a dependent under a family member, then once you become a responsible person your health insurance must be transferred to your own company. The NHI Administration cross-checks regularly; if it finds you have not transferred, it will require correction and back-charge premiums, and you will then have to sort out refunds for the duplicated months, which is far more trouble.