Killer+Sitter

A legendary mercenary, once feared as a killing machine on the battlefield, has arrived in Japan. He has taken on a new name: Ryuusei Nogawa. His mission is "to raise a baby." But Nogawa, who has never known a peaceful, quiet life, is struggling mightily with parenting for the first time!? To ensure the healthy growth of the mischievous Hoshina-chan, he must "legally" eliminate any dangers that come his way! A slice-of-life parenting story featuring the former strongest mercenary!

(Source: Kodansha, translated)