====== 0721 ======

This is a play on words, using the Japanese reading of the Latin letter O, which is オー (ō), for 0; for the digit 7, using first syllable of its kun'yomi; for the digits 2 and 1, using first syllables of their respective on'yomi. Finally, the word reads オナニー (onanī, “masturbation”).

Noun
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0721オナニー • (onanī) 

(slang) masturbation