Due to Ryohei's enthusiasm, he often rushes into things without fully evaluating the situation, which often ends in his injury. Every time he sees Tsuna and his friends doing something strange, he gets fired up and always wants to be a part of it. He even barged into a zoo, expecting to fight a bear, but ended up fighting a lion instead. As such, he prefers to fight his opponents head on, seeing any disadvantage as a chance to improve his fighting skills. His motto is to live "to the extreme!", which he applies to everything he does. Ryohei Sasagawa is Kyoko 's older brother who is obsessed with boxing. However, Tsuna and his friends are able to defeat Byakuran and the Millefiore and return to the past. It is later revealed that Byakuran has gained knowledge from parallel worlds and that he wants to obtain all the Mafia rings in order to obtain a power similar to omniscience. As Tsuna and the Vongola Guardians from his time fight the Millefiore they learn that Shoichi Irie, a comrade of Tsuna's future self, was the one who sent them to the future as the future Tsuna said they were the only ones who can defeat the Millefiore leader Byakuran. Later, after defeating the Varia, Tsuna and his friends are transported to the future where they must face the Millefiore Family, who are annihilating the Vongola. Lambo, a weak infant assassin who came to kill Reborn, and Chrome Dokuro, a girl who has a mental and physical link with the criminal Mukuro Rokudo, joins them as well. To defeat the Varia, Reborn recruits most of Tsuna's schoolmates to become the Vongola guardians: Hayato Gokudera, a dynamite expert who wishes to be his right-hand man, Takeshi Yamamoto, a baseball player who thinks the Mafia is a game, Ryohei Sasagawa, the energetic captain of the school boxing club, and Kyoya Hibari, the deadly head prefect. Later, The Varia, Vongola assassin squad, claim the right for their boss, Xanxus to be the true Vongola boss, and start a competition to decide it. Tsuna goes through many predicaments in his progress of becoming the Vongola boss including fighting against escaped Mafia convicts posing as Kokuyo Junior High students. He also starts making several friendships such as his crush Kyoko Sasagawa. Through his experiences, Tsuna unconsciously becomes stronger and more confident, which ultimately makes him better suited as the Vongola Family's boss despite continuing to reject his Mafia inheritance. Reborn's main method of teaching Tsuna is the "Dying Will Bullet", which will make the person be "reborn" with a stronger self intent on fulfilling his dying will. Tsuna then unwillingly undergoes training from Reborn. "Vongola IX", the current head of the family, sends Reborn, an infant hitman from Italy, to train Tsuna. For these reasons, Tsuna is the only remaining heir. Also, the other candidates for the position of the head of the Vongola Family have died. He is told by Reborn that he will become the tenth (Italian decimo) Vongola boss. Reborn enters and says that Chrome is in deep trouble, as it seems that Rokudo has been defeated.The Reborn! story revolves around a boy named Tsunayoshi "Tsuna" Sawada, who is chosen to become the Vongola Family's boss due to him being the great-great-great-great grandson of the first Vongola boss, who had moved to Japan from Italy during his time. While Tsuna worries about what to do, Lambo comes in and doodles on Tsuna's legs, making him angry and scream at Haru, who apologizes and leaves. Meanwhile, Tsuna finds out Lal's condition and starts to worry, but Lal Milch lectures him on 'choosing the right hell.' Ryohei meets up with Hibari to discuss the current situation and starts a quarrel. Byakuran finally reveals that Guido is also Mukuro, and they engage in a battle. Meanwhile, in Millefiore HQ, Byakuran has found out that Leonardo Lippi is an impostor whose real name is Guido Greco, a man who murdered 15 men and escaped from prison a year ago, similar to that of Mukuro. It seems that Yamamoto needs more training, and Gokudera has flaked off from his training.
As Tsuna trains thoroughly for the raid in five days, Lal Milch is experiencing problems due to the Negative Seven Rays, so she excuses Tsuna to check on Yamamoto and Gokudera.