Every time I peek at the code from something by Mr. Endoh, I end up down a rabbit hole and learn something. I look forward to what this one brings. Probably looking into this Piet language: https://www.dangermouse.net/esoteric/piet.html

Another awe-inspiring quine of his, from about a decade ago, is the 128-language ouroboros quine:

https://github.com/mame/quine-relay

The esolang wiki has a few simpler to grasp piet examples too. https://esolangs.org/wiki/Piet