The Assassin Was Reborn into a Fantasy World and Started Killing Randomly

The number one assassin in the Imperial City was killed after losing his usefulness after completing his last mission. "I worked hard for my country, and it's really ridiculous that I ended up like this." "Sorry, this is an order from a superior!" ............. That's it, nonono Real kawaii authors would not write like this. The protagonist is reincarnated into a fantasy world. The continent is full of spiritual energy. He uses spiritual energy to enhance his strength. A world where the strong is king. It's systematic. Don't ask why. I'm a newbie and I'm not very good at writing. Once I get stuck writing, it's easier to use the system... This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.