Jusaburō Mōri is a first-year high school student and former Rikkaidai Junior High tennis member, part of an undefeated national championship team the year before the current storyline. Known for skipping practices, he drew resentment from teammates Yukimura Seiichi, Sanada Genichirō, and Yanagi Renji, who felt he took tennis for granted during Yukimura's hospitalization. Yanagi specifically lacked substantial data due to Mōri's inconsistent attendance. In the prior year's national semifinals, he defeated Shitenhōji's Oshitari Kenya without conceding a game. After advancing to Rikkaidai High, he retained special treatment as a tennis prodigy but continued skipping practices. Following a decisive loss to Hyotei's Ochi Tsukimitsu at the Kantō Singles Tournament and an injury, Mōri considered quitting tennis. Witnessing Yukimura's determined rehabilitation in the hospital inspired him to recommit to rigorous daily training. During this period, he secretly left sports drinks for Yukimura after rehab sessions, earning the nickname "Sports Drink Fairy" from Yukimura, who remained unaware of his identity. His renewed dedication led to winning a newcomers' tournament without dropping a set, securing a U-17 Selection Camp invitation. At camp, he rose to become Japan's U-17 No. 10 player. Coaches paired him with Ochi to curb absenteeism, dubbing them "Super High School Doubles Specialists." Initially intimidated by Ochi due to their past match and Ochi's stoicism, Mōri developed deep respect, affectionately calling him "Tsuki-san." During the camp revolution, they faced middle schoolers Atobe Keigo and Niō Masaharu. Niō mimicked Tezuka Kunimitsu using techniques like the Zero Shiki Serve, which Mōri adapted to and returned. The match extended to three sets, with Mōri dislocating his shoulder strategically in the final set. They lost, leading Niō to temporarily claim the No. 10 spot. Mōri regained his position after Niō's camp departure. At the U-17 World Cup, Mōri partnered with Yanagi for the Doubles 1 match against France. Initial friction arose from Yanagi's lingering resentment, but Yanagi recognized Mōri as the "Sports Drink Fairy" upon seeing the same beverage, prompting reconciliation. During the match, Mōri entered a "Sleeping State" to enhance Yanagi's data collection, overcoming France's Delacroix and Saint Georges. Before the World Cup finals, he partnered with Ochi against Kimijima Ikuto and Tōno Atsukyō in an intra-ranking tournament doubles match, winning after Ochi awakened his true abilities as the former No. 4. Physically, Mōri stands at 191.63 cm, among the tallest Japanese players in the series. He is right-handed with an all-rounder playstyle, using a Dunlop Biomimetic M3.0 racket and Dunlop Hybrid Pro II shoes. His personality blends cheerfulness with occasional arrogance, especially during his initial Genius 10 tenure. He maintains playful match conduct, often taunting opponents, yet shows strong loyalty to Ochi and genuine concern for former Rikkaidai juniors.