Hime Kingyo no o Bako

The story takes place in what is now the Edo period, in a different dimension. The protagonist is a townsman living in a castle town. Having lost his parents at a young age, he makes a living helping out at a friend's dumpling shop. He is not wealthy, but he lives a fulfilling life. An unsettling atmosphere hangs over the town, and as the protagonist walks down a street at night, feeling uneasy, the monster appears before him. He is rescued and taken to Chiji Castle. Without knowing the circumstances, the protagonist is made a candidate for the castle's principal wife, and a strange life at the castle with his subordinate begins.

[Translated from Official Website]