By day, Romeo Maki is a respectable man who loves bringing gifts to the local orphanage, and Juliet is a newly employed nun working at said orphanage. However, by night, they are Masked Man M and Lady S, popular professional wrestlers. Kick-Heart tells the story of what happens when this dynamic pair meet in the ring, the only place where they can express their hidden desires.

After the intense quarterfinals, the U-17 World Cup competition has been whittled down to four formidable teams. Standing between Team Japan's quest for international glory is the nine-time tournament champion, Germany, and their star-studded team, pro player Jurgen Borisovich Volk at its helm. With both the momentum and the crowd's favor on the side of their opponents, Japan faces an uphill battle. Determined to avenge an earlier loss, Japan sends seven of their best—including team captain Houou Byoudouin—to challenge the German national team. But trying to reach the finals for the first time in Japan's tennis history may cause even these fearless players to crumble under mounting waves of pressure as they venture into uncharted territories.

Kenma Kozume has never considered volleyball fun or thrilling: it is merely something he is good at. But now Nekoma High School's volleyball team has qualified for the Spring Nationals and prepares to battle their long-standing rivals—Karasuno. Now, Kenma has to analyze the most confounding and resilient team and lead Nekoma to victory against them. Moreover, he will play against his friend Shouyou Hinata, Karasuno's short but incredibly proficient middle blocker. Karasuno has never been able to beat Nekoma in practice matches. Even so, despite his usual indifference, Kenma feels a tinge of excitement at the prospect of facing Karasuno in a high-stakes official game with no do-overs. To advance to the semifinals and ultimately restore their team's former glory, Karasuno must find a way to overcome Kenma's brilliant strategy and defeat Nekoma in their own territory.