Magic Gems Gourmet - Chapter 18.1 - A High-Class Magic Stone is Eaten.

A man was transported to Ancient China and eventually became a servant of a declining household without a male heir. He utilized his wits and modern knowledge to help the household and eventually become trapped in the sea of political turmoils of the period.

- Description from Novelupdates

In this era filled with countless wonderful talents, no one has any expectations for a pair of weak fists anymore!In the human world, there are swords that surpass all the heavens, spears that sweep away thousands of armies, fires that burn everything, and thunder that shatters the sky!Young people have too many choices, and everyone will move towards the most handsome, coolest, and most powerful!Only the stubborn boy chose to practice the fragile fists in front of him.Everyone thought he was crazy until the disaster struck.

「Shimizu-san, you dyed your hair black.」「Ah, yes.」「Why did you dye it all of a sudden?」「Because…yesterday…」Shimizu-san, who sat next to me and had dyed her hair from blonde to black gradually lowered her voice, slightly blushed, and laid her face down on the desk.

This is the story of a modern sailor who was accidentally reborn as a soldier of the Brazilian Expeditionary Force, and finally became the largest plutocratic family in Brazil by virtue of his foresight.

- Description from novelbuddy