6 decades books

The four continents of the world got combined into Ametar, the only continent in the world. Together they formed a country in the middle that has 5 nations. East of the country is Xou, where the strongest samurai lives. He is said to be immortal and his only goal is to kill himself. Knowing this, he makes children for the only purpose is to kill him. Why does he want to die so bad and how did he become immortal?