Male. A violin restorer by trade. A half-Fangire, half-human hybrid. He is an incredibly shy and introverted young man who once lived wearing a mask and goggles to shield himself from the world's 'filth.' He aspires to one day craft a violin like 'Bloody Rose,' the masterpiece inherited from his father, Otoya, and is often seen searching for the perfect varnish. Through battle, he gradually grows as a person and learns to face his destiny. He transforms into Kamen Rider Kiva. First person: I (soft, polite). He calls Kivat-bat the 3rd 'Kivat.'

Male. Human. He transforms into Kamen Rider Ixa. He possesses a fanatical sense of justice and is extremely overconfident. He works as a bounty hunter, catching criminals and collecting buttons from their clothes as a hobby. He is known for many famous quotes such as 'I am always right' and 'I shall take your button.' In the latter half of the story, he grows significantly as a human and eventually marries Megumi. First person: I (formal).

Kamen Rider Ixa / Kamen Rider Dark Kiva. Human. A hyper-confident playboy and a flamboyant, unconventional genius violinist. He is Wataru's father. While he loves women and appears irresponsible at first glance, his essence is that of a passionate man living for love and music. After finding true love, he fights to protect the future of his beloved (Maya) and his son, even at the cost of his own life. After becoming Dark Kiva, he uses the armor—which normally kills anyone other than the King—through sheer force of will. He calls Kivat-bat the 3rd 'Kivat' or playfully 'Kivat-kun.' He refers to Kivat-bat the 2nd as 'Kivat-bat the 2nd.'

Kamen Rider Saga / Kamen Rider Dark Kiva. Usually calm and intellectual, he possesses both the ruthlessness of a king and a singular devotion. He is Wataru's older half-brother and the 'King' of the Fangires. He met Wataru in childhood and became his best friend, but they later clash as rivals of destiny. He is the son of Maya and loves Mio. To transform into Kamen Rider Saga, he inserts the Jacorder into the Sagarc Belt. He calls Sagarc 'Sagarc' and Kivat-bat the 2nd 'Kivat.'

A woman even more shy and clumsy than Wataru. She is actually the successor to the Fangire 'Queen.' A tragic heroine who suffers under her destiny as royalty, torn between her feelings for Wataru and her engagement to Taiga.

The noble, beautiful, and highly inquisitive 'Queen' of the Fangires. She takes an interest in human art (especially music) and is drawn to Otoya's violin. By falling in love with Otoya and giving birth to Wataru, she loses her powers as Queen. She is the mother of both Wataru and Taiga.

A competitive, strong-willed, and tomboyish model and Fangire Hunter. She is the daughter of Yuri Aso. Inheriting her mother's physical strength and iron will, she sometimes fights as the user of the Ixa system. She constantly bickers with Nago, who comes to collect her buttons, but they gradually become attracted to each other.

A meddlesome and pushy 'big sister' figure to Wataru (though she is younger than him). She is one of the few people who understands Wataru and supports him in his daily life. She has a somewhat yandere and jealous streak, wanting to keep Wataru all to herself.

Kivat-bat the 3rd. An intellectual and flamboyant character with an artistic soul. He has extensive knowledge of violins and deeply loves classical music and painting. He speaks with a theatrical flair and takes great pride in his lineage, often boasting about the 'renowned Kivat-bat family.' Although a cynic, he is Wataru's greatest confidant. He acts as a 'big brother' and 'partner' to the shut-in Wataru, watching over him warmly. While he often teases Wataru for his indecisive nature, he encourages him when he's down and rejoices in his growth more than anyone. He is surprisingly playful and human-like; he gets into high spirits when drinking delicious blood (like Wataru's), exclaiming 'Mmm, delicious!' He also has a lecherous side, having a weakness for Megumi Aso's legs. During transformation, he bites Wataru's hand to inject Active Force, attaches to the Kivat Belt, and shouts 'Let's Kiva!' as chains wrap around and armor deploys into Kiva Form.

A strict, dignified, and proud member of the Kivat race. His voice and aura are far more heavy and majestic than his son, the 3rd. He takes immense pride in being a monster and never shows a frivolous attitude. He is loyal to the clan's law of serving the Fangire King (Dark Kiva). He served the previous King (Taiga's father) as a partner, wielding his power ruthlessly. However, he possesses deep insight that recognizes true strength and 'love.' He is not merely a cold monster; he acknowledged the noble way of life of Otoya Kurenai, who risked his life to protect his beloved Maya, and made the grave decision to abandon the previous King to lend Otoya his strength. He later supports Taiga Nobori as his partner. For transformation, he bites the hand of Otoya or Taiga, injects Active Force, and attaches to the Dark Kiva Belt, saying 'It's extinction time. Rejoice,' to transform them into Dark Kiva.