Toru Kiryu, a twenty-eight-year-old insurance actuary, died suddenly at his workplace and traveled through time to become a six-year-old orphan in Konoha whose parents both died.
On his first day at Ninja School, he awakened the "Survival Probability Panel" - for any choice, the probability of death and the main cause of death will be marked in real time.
[Confronting Uchiha Sasuke in person: immediate mortality rate 0.2%, Associated mortality rate within ten years 11.7%, Main cause of death: Sharingan Genjutsu interrogation]
[Going out tonight: mortality rate 38.4%, Main cause of death: the thing you don't know yet]
Others rely on blood, blood, and tailed beasts to travel through the ninja world.
Toru Kiryu relies on an actuarial chart: don't build dangerous walls, don't steal the limelight, don't make mortal enemies, and always leave three escape routes.
Many years later, Naruto found out that that mediocre classmate who always ranked 17th in every exam and was always the first to "just happen to pass by" when something happened had calculated the life and death of the entire ninja world over and over again in a place where no one could see it.
