Kenichi Shirahama, a timid high school student, begins the series as a frequent target of bullies due to his lack of physical strength and confidence. Seeking to change his life, he joins his school's karate club but quickly realizes that traditional training methods are ineffective for him. His life takes a dramatic turn when he meets Miu Furinji, a skilled martial artist who introduces him to Ryozanpaku, a dojo run by six eccentric martial arts masters, each specializing in a different discipline. These masters include Akisame Koetsuji, an expert in Jujitsu and a scientist; Kensei Ma, a master of Chinese Kenpo and a former assassin; Apachai Hopachai, a Muay Thai fighter with a gentle demeanor; Shio Sakaki, a karateka with a fiery temper; Hajime Shiba, a master of weapons and stealth; and Ryuto, a master of Shorinji Kempo and a former delinquent.

Under the guidance of these masters, Kenichi undergoes rigorous and often unconventional training to improve his physical and mental abilities. His journey is marked by numerous challenges, including battles against rival martial artists, members of the criminal organization Ragnarok, and other formidable opponents. Throughout the series, Kenichi's growth is evident as he transitions from a weak and fearful individual to a confident and capable martial artist. His relationship with Miu also evolves, with her serving as both a mentor and a source of inspiration.

The narrative explores themes of perseverance, self-improvement, and the importance of mentorship. Kenichi's progress is not linear; he faces setbacks and moments of self-doubt, but his determination and the support of his mentors and friends help him overcome these obstacles. The series balances intense martial arts action with moments of humor and character development, creating a dynamic and engaging storyline.

As Kenichi becomes stronger, he attracts the attention of various adversaries, leading to increasingly challenging confrontations. These battles test not only his physical abilities but also his resolve and understanding of martial arts principles. The series culminates in a climactic showdown with Ragnarok, where Kenichi must use all the skills and knowledge he has acquired to protect his friends and uphold the values of Ryozanpaku. Through his journey, Kenichi learns that true strength lies not just in physical prowess but in the courage to stand up for what is right and the willingness to grow as a person.