OVA
Description
Roswaal L. Mathers serves as the Margrave of Lugunica's western territories, head of the noble Mathers family, and the kingdom's Head Court Mage. His physical form conceals the soul of the original Roswaal A. Mathers (born Altair Mathers), who has possessed his direct descendants for over four centuries to pursue his objectives.

Born into nobility roughly 400 years ago, Roswaal A. Mathers possessed immense magical potential from youth, suffering debilitating pain due to unstable magic gates. Deemed a burden by his family, his fate shifted when Echidna, the Witch of Greed, stabilized his magic through physical contact (described as a kiss) and took him as her apprentice. Roswaal developed profound devotion to Echidna, her kindness contrasting sharply with societal rejection. This devotion defined his existence after the Holy Dragon Volcanica destroyed Echidna's body and confined her soul to a tomb.

To extend his life for Echidna's resurrection and Volcanica's defeat, Roswaal employs body-possession magic. Upon aging, he transfers his soul into a descendant, inheriting their physical form while retaining memories and magical power. His twelfth and current host is Roswaal L. Mathers, possessed at age 14. Previous incarnations include the tenth, Roswaal J. Mathers (female), who fought in the Demi-Human War. Each body displays heterochromatic eyes (yellow left, blue right), indigo hair, and flamboyant attire. The current host stands 186 cm tall, adorned with elaborate clownish makeup featuring purple lipstick and asymmetrical eyeshadow.

Roswaal orchestrates intricate schemes guided by Echidna's Tome of Wisdom, which predicts future events, aiming to align reality with its prophecies. Approximately 40 years before the main events, he adopted the orphaned oni twins Ram and Rem after the Witch Cult destroyed their village, recognizing Ram's potential to kill Volcanica. He sponsors Emilia's royal candidacy primarily to access Volcanica's blood through her, intending to use her, Subaru Natsuki, and Ram as instruments for Echidna's resurrection.

His manipulations include instigating conflicts with the Witch Cult to elevate Emilia's status, hiring the assassin Elsa to attack Emilia's camp, and summoning the Great Rabbit to slaughter Sanctuary inhabitants. These actions aimed to force Subaru to embrace Return by Death and fulfill the Tome's directives. During the Sanctuary crisis, his plan failed when Subaru burned the Tome and defeated him in a wager. Bound by an Oath Curse, Roswaal cannot harm Emilia's allies without risking permanent soul destruction.

Post-defeat, Roswaal shifts incrementally. He offers genuine support to Emilia after witnessing her overcome past trauma—a feat he could not achieve. He tolerates distrust from allies like Otto Suwen, provides combat guidance to Garfiel, and prioritizes protecting Subaru across borders. However, he retains his core ambition, warning Subaru that failure to prevent casualties will trigger retaliatory destruction. In later events, confusion surfaces regarding his role relative to Subaru's Authority, though he refrains from acting on earlier threats.

Roswaal wields the Divine Protection of Sorcery, granting mastery over all six elemental magics (fire, water, wind, earth, yin, yang). As Lugunica's strongest combat mage, his power rivals an army. Notable spells include fiery Goa, Ul Goa, and Al Goa; weather-altering Altemillion; and flight magic. His yellow left eye nullifies enemy spells. He also possesses martial prowess, demonstrated during Roswaal J. Mathers' tenure.

Relationships remain anchored by his obsession with Echidna, whom he seeks to resurrect despite her disapproval of his methods. He shares mutual respect with Beatrice, Echidna's artificial spirit creation, and protects Ram and Rem while viewing Ram as a weapon against Volcanica. His dynamic with Subaru evolves from manipulator to reluctant ally, acknowledging their shared determination despite conflicting methods.