The Rookie King Saga is the first story saga, and the first in the first part of the series.
Ippo Makunouchi was being bullied by Masahiko Umezawa, Matsuda, and Takamura when professional boxer Mamoru Takamura stepped in to help the boy. After being interested in boxing due to the event and wanting to know the answer to his question of "What does it mean to be strong?", Ippo gets accepted to the Kamogawa Boxing Gym after losing in a spar with Ichirō Miyata, which formed a rivalry between them. After winning a rematch spar against Miyata, the two promised to settle the score in the professional ring during the East Japan Rookie King Tournament. After easily passing the pro test against Naoya Ogawa to get the C Class License, Ippo's road to glory begins.
Starting off for Ippo's debut match, the easygoing fighter Yūsuke Oda, who lacks stamina and the appropriate mentality as a professional. Ippo successfully wins by knockout, and Miyata and another newcomer, Ryō Mashiba, also begin their boxing careers with a win in their debut match. Ippo then fights the dirty fighter Yoshio Fujiwara, in which Ippo outclasses easily. Afterwards, the East Japan Rookie King Tournament begins, and so with his opponents getting better, his training starts to become more difficult from his coach Genji Kamogawa so he can keep up.
He fights against Kenta Kobashi, a very much different boxer who is tactical and slow, then the rising star Ryūichi Hayami with his "Shotgun" technique and lastly Jason Ozuma who is known for his powerful hooks.
After the promise between Ippo and his rival Miyata was broken due to the latter losing in the semi-finals against Mashiba who has the Hitman Style and the troublesome Flicker Jab, for the finals, Ippo will be facing against the Flicker Jab user.
This fight has excited the west rookie king champion "Rocky of Naniwa" Takeshi Sendō, as he watched it live. He has been looking for someone like Ippo to brawl all this time. Sendō seeks to fight Ippo for the All Japan Rookie King Tournament in Osaka. Ippo injured his fist with the last match he had with Mashiba, needing some time to heal and also to prepare for Sendō's Sunday punch, the Smash. After the first two exciting rounds, as the third round was about to start, Sendō does not get up. The referee checks him and, he declares the victor to be Ippo. Sendō unconsciously stares down Ippo.
Ippo being victorious with all his fights so far, becomes the "All Japan Rookie King".