In the first episode of "Undead Girl Murder Farce" titled "Oni Slayer," the audience is introduced to a rich, imaginative world where folklore and fantasy intertwine. The central figure of the episode is Tsugaru, a mysterious character who is part human, part Oni (a mythological creature from Japanese folklore). Tsugaru is portrayed with a mix of liveliness and casual charm. His fondness for alcohol hints at a past that is as complex as it is dark.

The narrative kicks into gear when Tsugaru displays a compassionate side of his character by rescuing a cat from a hostile crowd. This act of kindness stands in contrast to a subsequent, highly stylized fight scene where Tsugaru faces off against a woman. Tsugaru's fighting style is flamboyant, showcasing impressive combat skills, but he maneuvers through the skirmish in a way that suggests he aims to de-escalate the situation rather than cause harm.

The plot takes a fascinating turn when it is revealed that the woman serves Aya, who is depicted as the only immortal being in this world—yet strangely, at this point, she is just a head. Aya expresses her desire for Tsugaru to end her immortality, and this serves as a catalyst for a deeper narrative that weaves together themes of life, death, and purpose.

As Tsugaru and Aya's head move through a beautifully rendered city, Tsugaru delivers an introspective monologue, grappling with his dual identity. His insights offer a glimpse into his inner conflict, as he feels neither fully human nor fully Oni and is frustrated by society's tendency to view him as a monstrous figure. He strives to challenge and change these perceptions.

By the end of the episode, Aya decides to assist Tsugaru in his quest to find her body, and the two form a partnership. This partnership is sealed in a somewhat eccentric manner with a kiss.