Nagito was born into a rich family, in the 28th day of the fourth month, with his birth month representing bad luck and death while his birthday represents a double amount of wealth and fortune according to old Japanese and Chinese beliefs. He was born with an extraordinary type of luck, and as a result, his life has always been shaped around moments of extremely good luck and extreme bad luck. The earliest known occurrence of this is when his pet dog was killed after being hit by a truck. His relationship with his parents is unclear; he mentions that they took him to an amusement park, but he also mentions offhand that his mother never complimented his appearance.
When he was only an elementary school student, Nagito and his parents went on a family vacation at San Cristóbal Island in the Galápagos archipelago. When the vacation was at an end, the family boarded an airplane leaving from the San Cristóbal Airport. However, the plane ended up being hijacked. Both the hijacker and Nagito's parents were killed in front of him after a small meteor crashed into the airplane, leaving him to inherit all of his parents' fortune and become free to do whatever he wished, as he had no other living relatives.
After his parents' death, during middle school, Nagito was kidnapped by a serial killer; he was released after the police found him (it was implied that the killer let him go after they found out nobody would pay the ransom). As a form of good luck, Nagito had discovered a lottery ticket in the garbage bag the murderer kidnapped him in: a winning ticket for three million yen.
These would be the first of many, many tragic things that happened to Nagito due to his luck. His cycle of good and bad luck made sure that any chance he might have at actual happiness would be spoiled. In order to cope with this, he developed a strong faith in hope so that he could find some meaning in his life. However, this turned into an unhealthy obsession. He didn't have any close friends or even acquaintances, as other people were disturbed by his strange way of thinking and he intentionally avoided other people in order to protect them from his bad luck. His bad luck caused the deaths of several people and he started to believe that only the people with "weak hope" could be killed by the influence of someone worthless like him. His luck cycle wore him down to the point of drifting through life without purpose, waiting to die and dreaming of becoming a stepping stone for the world's hope. Believing that he is unable to embody hope, he idolized Hope's Peak Academy and its' students as symbols of hope who are capable of creating "absolute hope" - hope that can overcome any despair.
As a teen, Nagito attended Spiral High School. He was diagnosed with lymphoma and frontotemporal dementia and was given a life expectancy of 6 months to a year (though, as it's later revealed, his good luck allowed him to outlive this). Though he claims he was fine with being alone before, he then realized he would die all alone and that he always desired, more than anything, to be loved by someone. After this, as a form of good luck, Nagito won a random lottery and was invited to attend Hope's Peak Academy. He refused at first, believing that he wasn't worthy, but the academy was adamant that they wished to study his luck, and he eventually accepted the offer.
Nagito joined Hope's Peak Academy's 77th Class and gained the title of the Ultimate Lucky Student. He was aloof and elusive, but was known as the self-proclaimed "Ultimate Ultimate Fanatic". According to Jin Kirigiri, the headmaster, Nagito meddled with the affairs of other students and caused nothing but problems. The headmaster was constantly burdened because of him and described him as an incredibly problematic child. However, he understood that the boy himself didn't really mean any harm, which was the worst part of it all.
During Nagito's second year, Junko started to manipulate students to join her Ultimate Despair. It's strongly implied that Nagito joined because he wanted to see Ultimate Despair's rise and fall, believing that no matter what, hope would always win and despair would be destroyed in the end. The members of the Ultimate Despair were brainwashed and fell madly in love with Junko. However, in Nagito's case, it was a bit different. He developed strange, conflicting feelings of both love and hatred for Junko and saw her as his sworn enemy.
