Reborn (voiced by Nishihagi Isuzu), who looks as cute as a baby, is actually a terrifying Italian mafia killer. He was ordered by the ninth-generation boss of Vongola to come to Japan to find the tenth-generation boss of Vongola, Sawada Tsunayoshi (voiced by Kunibu Yuka), and train him to be a qualified successor. Sawada Tsunayoshi is nicknamed "useless Tsuna". He is a student in Class A of the first year of Namimori Junior High School. His average score in all subjects is 17.5 points. He can only jump three layers on the vault horse and can't do a flip up on the horizontal bar. He is a useless person who can't do anything. Reborn's weird and extreme behavior makes Tsuna, who has always been sloppy and unmotivated, a headache. However, Reborn used the sure-kill bullet to make Kyoko Sasagawa (voiced by Yuna Inamura), the idol of Namimori Junior High School, develop a good impression on Tsuna, who has always been unknown. Tsuna slowly began to accept Reborn's transformation, lived a happy and terrifying life, and moved step by step towards the leader of the mafia.