MTL - Konoha: Rebooting Life of a Medical Ninja - Chapter 28 mermaid

In her previous life, she was humiliated and bullied every day. Her relatives despised her and her friends played tricks on her! Her mother and elder brother died one after another early. She gritted her teeth and survived the adversity alone, but only managed to live for twenty-six years!When she opens her eyes again, she finds herself back in time twenty years ago. To swallow insult and humiliation silently and let history repeat itself? If everything couldn't be changed, what was the point of her rebirth?! Who can stop her now that she defies her destiny and her abilities are emerging? In front of others, she is an ordinary student with an indifferent personality, isolated by her classmates. Behind their backs, she works step by step to build a brilliant and extraordinary business network.

Xiao Yu, who was a student from modern Earth, accidentally transports to another world and becomes the lord of a territory. Facing an unfavorable situation, he vows to take back his family business, build his new territory, kill all of those who covet his wealth, and dominate the world!

- Description from Novelupdates

Our protagonist Caam is a man from Earth that was reincarnated into this world as a demon. In order to survive, he spared no effort in avoiding the sparks of battle and without noticing it, he became strong himself.