"Romantic Killer" centers on Anzu Hoshino, a high school girl who prioritizes video games, chocolate, and her cat over romantic relationships. Her life takes an unexpected turn when a magical creature named Riri appears, claiming to be a matchmaking wizard. Riri forces Anzu into a "romantic simulation" to break her out of her comfort zone and push her toward finding love. Using magical interventions, Riri removes Anzu’s beloved distractions—her games, snacks, and even her cat—and introduces her to three potential love interests: Tsukasa Kazuki, a popular and kind-hearted classmate; Hijiri Koganei, a childhood friend with a playful demeanor; and Junta Hayami, a reserved and mysterious transfer student.

As Anzu navigates this forced romantic scenario, she resists Riri’s efforts, determined to reclaim her old life. However, her interactions with the three boys gradually reveal their individual struggles and complexities. Tsukasa, despite his popularity, harbors insecurities about his family’s expectations. Hijiri, though cheerful, hides feelings of inadequacy. Junta, the most enigmatic of the trio, struggles with his own past and emotional barriers. Anzu’s blunt and straightforward personality often clashes with the expectations of a typical romantic heroine, but her honesty and resilience begin to influence those around her.

The narrative explores themes of self-discovery, personal growth, and the complexities of relationships. Anzu’s journey is not just about romance but also about understanding herself and others. The series balances comedic moments with heartfelt scenes, as Anzu’s reluctance to conform to societal norms challenges the traditional tropes of romantic storytelling. Through her interactions with Tsukasa, Hijiri, and Junta, the story delves into the idea that love and connection are not always straightforward but are shaped by individual experiences and vulnerabilities.