Senki to Yobareta Otoko, Ouke ni Ansatsu saretara Musume wo Hiroi, Issho ni Slow Life wo Hajimeru: Innocent Days

The kingdom's mercenary Ordoll, also known as the "War Demon", is feared by enemies and allies alike. Although he always distinguished himself no matter what the battle, he is "assassinated" the day after a ceasefire agreement with a neighboring country is concluded. After pretending to be dead, he manages to escape and decides to head home, shaving his beard and shortening his long hair. Immediately before arriving at the village, Ordoll picks up a 5-year-old little girl who calls him her "papa." The strongest mercenary, who suddenly becomes the father of a 5-year-old daughter despite being unmarried, eventually develops into the strongest parent!

(Source: Earth Star Entertainment, translated)