How is this an axis? I thought that the opposite of Grim is Cheery and the opposite of Noble is Base (as in being a cad).
Trope Workshop talk:Setting Alignment
Grim - Noble?
Probably supposed to refer to the worldview?
It's fan-speak, it just happened to turn this way. The scales were rather obviously derived from the term "Grimdark", so these two ends were "fixed". Thus it's like this mostly "for historical reasons", which is fairly common for slang.