六つ
むっつ · muttsu · JLPT N5 · noun
six (things)
6️⃣ mu (six) + tsu (native counter): mu doubles its t, giving mut-tsu
Native Japanese counting adds the generic counter tsu to an old number root. Six is mu, the same root as in muika (the 6th day). The t doubles, so it is muttsu, not mutsu. It pairs with mittsu (three): mi doubled gives mu.
六 — top stroke 亠 + 八 (eight/split)
Originally a pictograph, possibly depicting a hut or shelter, but its early meaning was lost. It was borrowed phonetically to write the number 'six'. The modern form shows a top mark 亠 over 八, but this structure is not semantic — it's purely a loan character for the numeral.