Seraphim, commonly known as Sera, is a vampire ninja forged by her village's century-long conflict, which instilled her initially cold demeanor. Seeking to serve Eucliwood Hellscythe, she arrived at Ayumu Aikawa's residence only to be rejected; she then became Ayumu's reluctant, nominal servant. Her core mission involved escorting or eliminating Eucliwood to prevent Megalo incursions into the human world. However, she ultimately defied assassination orders after developing genuine loyalty, leading to her execution by superiors and subsequent revival through Eucliwood's blood. Physically, Seraphim possesses long black hair, usually secured in a high ponytail with loose strands framing her face. Her green eyes shift to red when utilizing her powers. She has a notably tall, slender build (173 cm/5'8") with a prominent bust, frequently accentuated by sleeveless tops and midriff-revealing outfits. She wears a cross necklace used during blood consumption. Her abilities blend vampire and ninja traits: teleportation via dispersing leaves, conjuring leaf-based katanas and energy blasts using the Tsubamegaeshi sword style, flight with wings formed from leaves, and inducing paralysis through anesthetic kisses preceding blood consumption. After ingesting Eucliwood's blood, she gained the power to unleash violin-based sound attacks capable of destroying Megalo. As a vampire, she requires periodic blood intake but avoids kissing males due to her clan's marriage customs. She exhibits enhanced strength, agility, and durability, though her cooking skills are notoriously poor, causing severe reactions in those who consume her food. Relationships define her development: she initially verbally abused Ayumu with insults like "dung beetle," citing disgust for his zombie nature and perceived perversion. Gradually, she displayed concern—fighting alongside him against Kyoko and the King of the Night, anxiously awaiting his recovery after critical injuries, and eventually admitting his home felt like her own. Her devotion to Eucliwood evolved from duty to authentic protectiveness, culminating in disobeying orders to harm her. With Haruna, she maintained a respectful rapport, using kiss-based anesthesia to feed without causing discomfort. Romantic feelings for Ayumu emerged later, intensifying her tsundere behavior through accidental intimate situations. Seraphim's character development shows progression from detached warrior to integrated housemate. Early hostility stemmed from wartime trauma and strict honor codes, but cohabitation softened her into acknowledging camaraderie. She retained core traits like loudly praising her sword style and upholding ninja traditions, yet began openly smiling, participating in domestic tasks like laundry, and expressing vulnerability. Her defiance of assassination orders marked a pivotal shift from blind obedience to moral autonomy, reinforced when Eucliwood revived her. By the narrative's conclusion, she balanced combat readiness with unwavering loyalty to her found family.