Junior high student Tsuna is a failure at school, sports and socializing. But when toddler assassin Reborn arrives to groom Tsuna for his future as a Mafia boss, Tsuna may have found the „magic bullet” he needs to turn his life around!
Tsuna is targeted for assassination, so a weapons tuner for the Vongola Family arrives to upgrade Reborn's arsenal. This winds up creating a fair amount of chaos, but it's summer and Tsuna soon finds other distractions--learning to swim, taking part in a summer poetry contest, plunging into the ocean to rescue a girl in distress, and defying a ghost bent on taking him to the „other side”!