steal
偸 centers on taking something secretly or without permission: stealing.
偸 combines 亻 (person) with 兪, which likely contributes the sound and may relate to the idea of stealth or taking. The exact historical development is uncertain.
A person 亻 beside 兪, which looks like a sneaky figure with a knife 刂 and moon 月, sneaking under moonlight to steal.
For ツ, imagine a thief stealing two (ツー) items under the moonlight: two -> ツ.