It’s interesting to note that there are two different kanji for the word koji in the Japanese language.
The first, 麹, is the earliest known written character for qu/koji, composed of a left radical for wheat (麦) beside the character for chrysanthemum (菊). This kanji comes from Chinese origin, and is used for koji made with any substrate.
As for the second character,糀, combines the character for rice (米) and the character for flower (花). As opposed to the first kanji this one originates from the Japanese language, and representative of how the fluffy white hyphae on finished koji cover the surface of the steamed rice like a flower; but also the rice blossoming into something more elegant and desirable. This character specifically is used for koji made out of rice.