This is a story a below-average boy named Tsunayoshi Sawada (nickname: "Tsuna" or "No Good Tsuna") that find himself to be the next boss of the Vongola Family, the most powerful Mafia organization. A home tutor named "Reborn", the most powerful Vongola hitman was sent to Tsuna to make him a respectable boss. And there starts the journey along with his friends.
