This led me to an unexpected rabbit hole - https://en.wikipedia.org/wiki/Intellectual_property_protection_of_typefaces

Typefaces (font styles) do not receive IP protection in USA, but it does in some European countries. However, computer fonts can be protected, being considered part of a software program, not unlike Photoshop. That means that you could, in theory, create identical fonts, give it a different name and license, and call it a day - so long as you can prove you didn’t just flip the font files or something.

Since the post is about Japanese fonts, here’s an old (2007) study done on Japanese law and typefaces - https://www.iip.or.jp/e/summary/pdf/detail2007/e19_05.pdf

Over 30% of typeface designers (34.6%) answered that they have discovered problems related to the theft of a design of a typeface they have created. There are various forms of theft, including the selling of similar fonts by companies that have not concluded a license contract, publication of similar typefaces as the creations of third parties, and distribution of pirated fonts that have been made based on the original typefaces. In addition, over 20% of designers (23.1%) have experienced problems such as violation of a contract with regard to typefaces they have created

in making a typeface into a font, a designer claims that “the typeface is his/her own creation,” and the designer and a font vendor conclude some sort of license contract for the typeface as a commercial practice; however, the method of handling the infringement of typefaces by third parties is seen as a problem since there is no clear legal protection for typefaces, which are the object of such contracts

According to this law firm, fonts would currently fall under Japanese Design Law - https://monolith.law/en/general-corporate/copyright-special-issues-japan