phenomen a book

A boy who was born in a modern fantasy in the year 500 and has a disability with little mana so he cant use magic almost at all so he becomes a knight even tho he dosent want to but its the closest thing hes good at [If you wonder what the flip is the first chapther is about its about his WHOLE LIFE this story starts from the start when he was born so thus story will be long and detailed as best as i can]