The line comes from Nanami Kento, the calm and methodical sorcerer in Jujutsu Kaisen, the manga and anime series by Gege Akutami. In Japanese, ato wa tanomimasu roughly means I leave the rest to you, a polite way of handing over unfinished work. Fans clipped the delivery because it fits Nanami's composed personality so well, and it spread through anime edits and meme videos where a character exits after doing their part. It remains popular because the phrase is short, instantly recognisable to fans, and works as a dry, understated ending to almost any scene.