Where does “真木” come from?

真木 (Old Japanese) comes from Old Japanese 木, from Proto-Japonic kəy — tree.

Ancestry of “真木”, step by step

Step	Language	Word	Meaning
1	Old Japanese	木	a tree or shrub; wood, timber, lumber; Combining...
2	Proto-Japonic	kəy	tree

真木 — Etymology, Origin & Word History | Etymology Explorer