MTL - The Life Through Books of the Salted Fish Family - Chapter 1 no money in hand

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

Tenjou Yuuya has been a bullied boy since the past.He lives in the home of his beloved grandfather while he goes to school. As usual, he receives a harsh bullying, and he takes an extended absence from school to have some time to heal his wounds.While on this long time of absence, he takes the opportunity to clean his grandfather’s house and goes to a room he never went before, where his grandfather keep many different objects that he gathered from his travels around the world. While he was arranging the objects, he found a door not on a wall among the objects.Out of curiosity he opens this door, what he found on the other side was…

An ordinary student, a wretched peeper, a cowardly teenager with a kind heart. In a terrorist attack, he inherited the knowledge of countless elites, embarked on a path of God Jagged Tu…

He is an artist!

He is a mathematician!

He is a psychology Doctor!

He is a master of fighting!

In fact, he is a man

Taken off raw site:

A wretched, dirty young man is working during the summer when he was caught up in a mysterious explosion. After that explosion, the young man is then left with the memories and knowledge of dozens of the world’s experts.

He has changed, his heart has become cold, iron-blooded. He became a killing machine, his mind turned mechanical, calculative. Everything goes according to his plans and calculations!

In this magical, slaughterous world, a door is opened for him…

- Description from Novelupdates