Kindergarten Wars 

Rita is Convict 999, a former legendary assassin who now works at a kindergarten for the children of world leaders. Her job is to protect the schoolchildren from the clutches of would-be assassins sent after them! But even with her overwhelming strength, Rita has a weakness—she’s head-over-heels for good-looking men!  (Source: Yen Press) Note: Third place at the 9th Next Manga Award in the Web Manga Category in 2023.