Masakatsu Hiyori hails from Inakuni Island and joins Inakuni Raimon as a defender when the team moves to the mainland to compete as Raimon Junior High in the Football Frontier tournament. He possesses slightly tanned skin, blue eyes, and distinctive white hair flowing outward on both sides. His casual outfit features grey boots, grey dungarees, a white jumper with yellow stripes, and a grey hat. Serving as the team's moodmaker and straight man, Hiyori frequently delivers quips, particularly targeting his senior teammate Goujin Tetsunosuke about the naming of hissatsu techniques; he famously compares Goujin's "Fire Lemonade" to the established "Fire Tornado." This dynamic continues throughout matches against teams like Eisei Gakuen and Tonegawa Tousen, with Hiyori providing commentary on Goujin's actions, stamina, and technique names.

Hiyori's involvement starts in the series premiere when he questions Norika Umihara's unusual behavior and later discusses the team's disbandment fears and mainland prospects with teammates near a cliffside. He expresses surprise upon learning the original Raimon team is inactive after arriving at Raimon Junior High. His soccer development includes learning his first defensive hissatsu, Shooting Cut, during coach Zhao Jinyun's training before the Mikage Sennou match. He later uses Shooting Cut to intercept Nosaka Yuuma's "King's Lance" against Outei Tsukinomiya, passing the ball to Haizaki Ryouhei. He participates in combination techniques, notably forming "Gravity Cage" with Hattori Hanta and Okuiri Hiro to stop "Koutei Penguin 2gou" during the Teikoku Gakuen match, contributing to Inakuni Raimon's 4-3 victory. He also scores one recorded goal in the Football Frontier tournament using a combination technique initially proposed for Michinari Tatsumi and Goujin against Eisei Gakuen, an action that inadvertently causes tension with Goujin.

During *Orion no Kokuin*, Hiyori attends the Inazuma Japan roster announcement but is not selected. He later appears at a surprise party for the departing members, where Goujin gifts him a Kappa bear keychain. After the Football Frontier International tournament, he returns to Inakuni Island with his teammates. He competes in the Football Frontier Autumn Tournament with Inakuni Raimon, facing the original Raimon team in the series-concluding match. His known hissatsu techniques include the defensive "Shooting Cut," the cooperative block "Gravity Cage," "Flash Dance," and supportive techniques like "Mikage Sennou (Asuto-hen) Killer" and "Kaze no Kokoroe" as documented in game materials.