Shortly after winning the World Martial Arts Tournament and using the winnings to pay off her grandfather's one hundred million yen debt, a reporter shows up on Kizuna Todoroki's doorstep. Impressed that such a young girl was able to defeat the 10-year reigning champion, the reporter wants to interview Kizuna for a piece on her and the Wadachi Ju-ken school of martial arts founded by Kizuna's grandfather.

However, before the interview can end, challengers begin to appear at the Todoroki household. After hearing that Kizuna is only 12, they hope to defeat her before her 13th birthday to usurp her position as the world champion. As dozens of challengers appear, Kizuna struggles to bring them all down, while the reporter learns more about the Todoroki family.