This story take place in REBIRTH UNIVERSE in  continent of Asi (a large piece of land) where different cultures were growing it was a peaceful period culture of Asi was somewhat similar to Japan with Shinobi's and Samurai were present there and were a tradition, these two became the factions and created many strong county's in Asi continent.

A man in samurai armour holding a Katana slashes and kills several mens,this man is Nobunaga the leader of Oda clan the elite samurai clan which was attacked by Shinobi's of Ega clan (A Powerful Shinobi Clan) this attack Eliminated whole Oda clan exept Nobunaga and his son who was born that day.

Killing several mens, Nobunaga reached at a room with a stone standing on top of that stone standing a Samurai sword was placed this sword has it's own history This was the sword in which Asura (The first Demon) was sealed Nobunaga takes the sword from stone standing and Extracts Asur's  Soul with help of Death exchange art (this consumes the life energy of user to give a large amount of energy in return) and put's the soul in his son to give him life because his child was born but was not taking breath after putting Asur's Soul energy in his son his son came back to life but Nobunaga's life energy was failing at last he says goodbye to his newly born baby and fade away.

Boy started crying,

After hearing his sound a Shinobi named Iziko came in the room seeing the boy all alone in the room Iziko thought of killing the boy and pulled out is Katana, but couldn't kill the baby his innocent face was enough to convince Iziko, who was a Master of Shinobi (A rank given to Shinobi master) took that boy to Oda a Shinobi country although Iziko was unmarried so when his friends and clan leader Sarama asked about boy he told them that this is his son whose mother died in child birth and now he will look after him Iziko named him Kirito.

From the early age Kirito was a quick learner and a quite boy who never speaks of not need.

Kirito aged with time and turned 5 years old, In Oda Country young boys and girls of age 5-6 are put in Ninja school to learn the ways of Shinobi.