Wow, and here I am thinking that Etzali was some low-level Magician, I guess a grimoire or two can really up ones' power level.
Remember people, nothing in toaruverse is completely random, even their magic have some history to it. The "
Rabbit and Moon" refers to one of two Aztec god/goddess.
Metztli -Queen of the Night- she feared the sun because she feared its fire. Also referred to as the lowly god of worms who failed to sacrifice himself to become the sun, and became the moon instead, her face darkened by a rabbit.
The other god is
Tecciztecatl -old moon god- he could have been the sun god, but he feared the sun's fire, so
Nanahuatzin became the sun god and
Tecciztecatl (in the form of a rabbit) was promptly thrown into the moon.
As for why human bones can be subsitute...I'm going to assume maybe rabbits in Aztec myth can be used to symbolize humans? Or maybe something more scientific, like the two share similiar bone density.