Pretending To Be God - Chapter 15: Letters

Samuel, a high schooler, got summoned with his classmates to another world as prophesied heroes. He expected glory, adventure, and a chance to save a kingdom. But those hopes were shattered when he discovered the truth, they were sacrifices, the gods who summoned them are no saviors, but monsters that feed on human souls. Among the victims is his little sister, dragged into the summoning by accident while she was delivering his lunch. Betrayed and marked for sacrifice, Samuel survives andmade a deal with (Arithmos) the God of war, with its power, he now vows to destroy every god and declares to take everything from them.

Freely traverse between the city and the abyss, cultivate a demon legion! Command demonic talents!My name is Bai Yan, from that day on... one of my souls possesses two identities.I am a demon! Also a human!When I am good, I benefit the world! When I am evil, there are corpses everywhere!

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