Harapeko Maou to Horyo Yuusha! Maou ga Ore no Heya ni Meshi wo Kui ni Kurun da ga

A world where humanity has been defeated by demons. The hero will spend his time in a cell in the Demon King's castle, but... "Hero-san, I'm hungry!" Why are the hero and Demon King eating together?! The Demon King comes rushing in almost every day. He ate meals with his supposed nemesis, sometimes played with him, and talked about trivial things. The new daily life is somehow ticklish, gentle, and warm. The hero who had been keeping his guard up gradually begins to open up...? You can't take your eyes off their slow-going relationship that will make you want to watch it forever!

(Source: Starts Shuppan, translated)