Negative interest rates are nothing more than a tax on wealth. These are semi-voluntary taxes paid by banks, savers, and investors. That’s it. The manner in which the tax is calculated results in some bleed-over effects into corporate debt, but that’s a taxation based disincentive to save. It’s just a tax.
Interests haven’t gone negative in five thousand years of recorded history in absolute terms, but they definitely have in interest + tax terms. It’s just uncommon.