Tsunayoshi (Tsuna for short) was a boy who was good at nothing, Hence why his nick name was 'No good Tsuna'. That all changed the day Reborn arrived in Japan,under guise of the home tutor, Reborn came to train Tsuna to be the 10'th boss of the Vongola; the most powerful mob Family in the world. Being the great-great-great grandson of the first Vongola he was chosen by the 9th to be his predecessor.
When Reborn arrives he tells Tsuna that him being his school "tutor" in a ploy to hide is real objective, train him to be mob boss. Tsuna at the time did not believe that Reborn was apart of the Mob and thought it was all just a joke, but that changed the next day when Reborn Tsuna revealed he had a crush on the schools popular girl, Kyoko Sasagawa. After Reborn,tells Tsuna he had a loser complex for not admitting his affection for her, shot Tsuna with the Dying Will Bullet; someone who is shot with said bullet will be resurrected with there dying will after dying, which works by using the pressure he faces doing a crisis to remove the bodies external limiters, giving him powers far beyond that of a normal human. Tsuna then, with his dying will confronted Kyoko and asked her to go out with him (his boxers being his only attire a the time) Kyoko, is horrified by Tsuna and he is called a "hentai".
Day Life arc