Fuuma Yousuke is a central character who serves as the primary love interest for the series protagonist, Hanasaki Momoko. He is a first-year student at Hanazono Academy and the star goalkeeper for the school's soccer team, a position that brings him considerable recognition among his peers. His birthday is October 31st.

Upon his first appearance, Yousuke comes across as rude, arrogant, and argumentative, bickering frequently with Momoko whom he teasingly nicknames Momopi. However, beneath this superficial exterior lies a genuinely kind, caring, and mature young man who is deeply protective of his friends and teammates. He is notably tolerant of Momoko's often bizarre behavior and shows great loyalty to those he cares about. This contrast between his teasing nature and his underlying sincerity forms the core of his personality.

Yousuke's role in the story becomes significantly more complex when his true heritage is revealed. He is a half-devil, having inherited devil blood from his father, Uragano, who was the legendary leader of the Rafaal Tribe in the Devil World. His human mother works abroad in Paris, leaving Yousuke to live alone in an apartment from a young age after his father, who worked as a ship captain, disappeared following a fateful voyage. His motivations are driven by a combination of his everyday life as a student and athlete, and a deeper, more profound need to understand his identity. When he learns of his father's death at the hands of devils under the command of the queen of the Devil World, Reine Devila, his primary motivation becomes a quest for vengeance and a struggle to come to terms with his cursed lineage.

Yousuke's key relationships are central to the plot. His most important relationship is with Momoko Hanasaki. What begins as a love-hate dynamic of constant bickering slowly blossoms into a profound romantic connection. Their relationship is complicated by their opposing natures, as Momoko is later revealed to be half-angel, making their love a forbidden bond between two worlds that are destined to be enemies. He is also a close friend of Yanagiba Kazuya, the captain of the soccer team, who acts as a mentor and confidant. Through his association with Momoko, he also forms strong friendships with her best friends, Yuri Tanima and Hinagiku Tamano.

Yousuke undergoes significant development throughout the series. Initially unaware of his devil heritage, he eventually discovers the devil powers that lie dormant within him, an ability that first manifests as a glowing blue aura when he instinctively shields Momoko from an attack. He is later forcibly transformed into his devil form, known as Viento, which gives him longer, spiked hair, a blue bodysuit with a crest, and a long cape. Initially, he is horrified and depressed upon learning he is a devil, pushing Momoko away in his despair. However, he learns to control his transformation and wields his power not for evil, but to avenge his father and protect Momoko and the human world. In the final battle, he and Momoko use the power of their love wave to purify Reine Devila. Following the conflict, Yousuke's devil powers are sealed so he can live a normal, peaceful life as a human with Momoko.

In terms of notable abilities, Yousuke is an exceptionally skilled soccer player, particularly as a goalkeeper. As a half-devil, his primary ability is the transformation into Viento. In this form, he wields a black sword and possesses enhanced strength and combat skills sufficient to battle powerful devils. His powers are often linked to his emotions and his connection to a bell given to him by his father, which glows or rings in the presence of devils or danger. The ultimate expression of his power is the creation of a love wave when combined with Momoko's angelic powers.