For the sake of Vongola and for the sake of Ten Dai Vongola, Reborn, Vongola's outside advisor and Ten Dai's tutor, the strongest Rainbow Son and the world's number one killer, gave up his relationship with Tsuna, forcing Tsuna to get engaged to a girl from the Elk family. Later, with the help of successive generations, Tsuna became the strongest leader and successfully defended his own happiness...