Extreme! Passionate Brother! is the 7th episode of the Katekyo Hitman Reborn! anime.
The episode starts in a ring inside Namimori Middle School's boxing club with the captain of the karate club Ushio Ooyama knocking out a boxing club member, Ooyama then asks if there are any stronger candidates. A white haired boy then arrives at the scene and challenges Ooyama, it is revealed that this boy is the captain of the boxing club. The boy then proceeds to dominate Ooyama in mere seconds, he then shouts "Extreme!", pumping his fists into the air.
We then move to a scene with Tsuna, Gokudera, and Yamamoto walking to school with Lambo trailing along beside them equipped with an arsenal of heavy weaponry which Yamamoto thinks are children's toys. Lambo then asks where Reborn is. Reborn proceeds to deactivate his Shadow Technique camouflage and reveals himself to Lambo, who decides to begin his assault on Reborn right then and there, but not before being fed a cake with a hidden grenade. The explosion sends Lambo flying away as Yamamoto exclaims how children's toys these days are so well-made. Tsuna suddenly remembers his promise with Kyoko to arrive early at school that day to discuss their social studies project, he then laments on the fact that he won't make it on time. Reborn proceeds to shoot Tsuna with the Dying Will Bullet and watches Tsuna run away in Dying Will Mode leaving Gokudera and Yamamoto to realize Tsuna forgot his bag.
Coincidentally, the white haired boy from earlier on in the episode encountered Tsuna on his way to school and managed to grab onto Tsuna's wrist, only to be dragged all the way to the school. After losing Dying Will Mode, Tsuna realizes he dragged someone with him and asks if the boy was hurt. The boy then requests for Tsuna to join the boxing club, saying he "needs someone with the amount of passion" Tsuna has, recalling the events of Tsuna's match with Kensuke Mochida and the Volleyball Tournament. Kyoko runs towards the pair, revealing that the white haired male is her big brother Ryohei Sasagawa.
Ryohei brings Tsuna to the boxing club, where Tsuna is met with Reborn disguised as Elder PaoPao, a Thai boxing elder. Reborn then says he wants to see Tsuna have a boxing match against Ryohei, to which Ryohei agrees. Tsuna is then dragged into the ring.
Reborn shoots both Tsuna and Ryohei, forcing both to enter Dying Will Mode, Tsuna however, gains the upper hand and knocks Ryohei out of the ring. Ryohei gets up, apparently fine, but before the two can finish their match the karate club comes back to have a rematch against Ryohei, which becomes one big brawl between the karate club members and Tsuna's friends. Ryohei and Tsuna finish off Ushio Ooyama and his older brother, Daigoro Ooyama, Tsuna this time with a counter and emerges victorious. Reborn states that a passionate guy like Ryohei is needed for the Famiglia.
The episode ends with Hibari threatening to bite the karate club members to death if they don't stop crowding.