Seraphim possesses a deep passion for the Tsubamegaeshi Sword Style (dubbed as Swallow Return Strike), often seen enthusiastically praising its techniques and principles. Honorable and chivalrous, she remains dedicated to her identity as a ninja, adhering to a strict code of conduct. However, this dedication often manifests as rudeness, particularly towards Ayumu Aikawa, whom she frequently refers to as a “piece of shit” (クソ虫, kusomushi, meaning “dung beetle”) or “disgusting.” In the English dub, she opts to call him a “maggot.” She openly expresses her disdain for his Masou-Shoujo outfit, claiming that a part of her soul dies each time she sees him wear it. Seraphim acknowledges her abrasive nature, attributing it to her upbringing in a village embroiled in conflict for over a century, suggesting that such an environment tends to breed a less-than-friendly disposition.

Beneath her tough exterior, Seraphim demonstrates genuine concern for Ayumu’s well-being. She volunteers to assist him in battles against formidable foes like Kyoko and the King of the Night, showcasing her loyalty and protective instincts. Her emotional evolution becomes evident when, after returning from a search for Eucliwood, she expresses happiness at being back home—an indication that she now considers Ayumu’s house her true home. This moment marks the first time she smiles warmly in the series, breaking her usual frowning demeanor.

Initially sent with orders to assassinate Eucliwood, Seraphim’s journey takes a significant turn as she develops a strong bond with her, ultimately defying her mission out of genuine care. This conflict with her duties leads to her being hunted and killed for her insubordination. However, Eucliwood resurrects her shortly after, allowing her to reconcile her actions when the context of her mission changes.

In addition to her ninja skills, Seraphim harbors a fondness for playing the violin and shows a determined effort to learn how to cook. Unfortunately, her culinary creations tend to be disastrous, with one such attempt even causing Ayumu to faint. As the series progresses, particularly in Season 2, her tsundere tendencies emerge, hinting at deeper feelings for Ayumu. Although she becomes friendlier over time, she still retains her critical stance toward his persistent perversions, punishing him in Episode 9 when he finds himself in an accidental compromising situation with Naegleria.

Ayumu Aikawa
Initially, Seraphim and Ayumu shared a passively hostile dynamic. Seraphim can be characterized as a tsun-tsun among the tsunderes, often exhibiting a mix of irritation and care. Ayumu initially views her as just another strange presence intruding on his life. However, as time passes, he becomes accustomed to her quirks and hostile mannerisms, eventually considering her a trusted friend. He learns to accept her cruel behavior as an integral part of her personality, never truly attempting to change her.

Seraphim starts off looking down on Ayumu, perceiving him as less than an animal, yet she develops a sense of trust in him during critical moments, believing in his ability to make the right decisions and handle the consequences. The depth of her feelings for Ayumu is hinted at when Kyoko comments on her emotional state during her parole, suggesting that Seraphim may be masking her true feelings for him. This observation goes unchallenged, indicating a level of awareness about her own emotions.

Despite their initial antagonism, Seraphim grows to genuinely care for Ayumu, though she continues to refer to him as a “piece of shit.” Her feelings for him become more apparent in Season 2, especially during moments where her emotions shine through, such as when she blushes after he eats her cooking (Episode 4) and her acknowledgment of being in love with him by Episode 8. Seraphim’s relationship with Ayumu transitions from a combative one to one filled with unspoken affection and camaraderie.

Sarasvati
Sarasvati is a fellow vampire ninja and serves as a senpai to Seraphim. Their relationship involves Sarasvati giving orders and advice to Sera, often acting as a mentor figure. At times, Sarasvati does small favors for Seraphim, such as delivering items like the ‘ero-glasses,’ a basket of questionable mushrooms, and a beef recipe intended for Ayumu.

Sera’s behavior can be seen as partially influenced by Sarasvati’s character, showcasing a blend of mentorship and camaraderie. However, Seraphim expresses disdain for Sarasvati’s idol-like persona, as it starkly contrasts with their customs as ninjas. This refusal to align with Sarasvati’s more flamboyant lifestyle underscores Seraphim’s commitment to her identity as a ninja, while also hinting at her desire to forge her own path separate from the expectations of her peers.

Plot: The Vampire on Ayumu’s Doorstep

Seraphim arrives at the Aikawa residence after a lengthy search for Eucliwood’s whereabouts. She immediately declares her intention to serve Eucliwood, hoping to be taken in as her servant. However, Eucliwood swiftly rejects her offer. Undeterred, Seraphim decides to stay overnight at Ayumu’s house, wary of him potentially usurping the role of Eucliwood’s servant. To assess his worthiness, she tests Ayumu’s resolve and capabilities.

Their initial conflict culminates in an unexpected turn of events: Seraphim chooses to become Ayumu’s servant instead, although she is not eager to forge a friendly relationship with him right away. Despite this rocky start, she quickly integrates into the household, joining Eucliwood and Haruna as Ayumu’s companions.

Throughout her stay, Seraphim contributes to the group’s efforts in battling various Megalo, showcasing her skills as a vampire ninja. She gradually begins to bond with her housemates, participating in casual hangouts and light-hearted interactions with Ayumu and Haruna. Her evolving dynamic with the group reveals both her commitment to her duties as a ninja and her growing affection for her new companions, particularly Ayumu. As the story unfolds, Seraphim’s character evolves from a lone wolf with a stern demeanor to a valued member of the Aikawa household, navigating the complexities of friendship, loyalty, and her own feelings.