Shadow Slave: Winter Samurai

I read a lot shadow slave fanfictions then I decided to create my own. Mc will be overpowered but not too overpowered. He can basically defeat anyone in the same rank as him but he won't go off and kill saints as a sleeper. Am not sure about romance. Anyway, this is my first book and English is not my first language so am bound to make some mistakes. P.s, this isn't my image. If the owner wants me to take it down, he should talk to me.