"Carnival Phantasm" is a comedic spin-off series that brings together characters from various Type-Moon franchises, primarily "Tsukihime" and "Fate/stay night," in a lighthearted, parody-driven narrative. The series is structured as a collection of short, episodic skits rather than a continuous storyline, blending absurd humor, meta-commentary, and playful interactions between characters.

The central setting is a whimsical carnival where characters from different universes coexist, often engaging in exaggerated and comedic scenarios. Shiki Tohno, the protagonist of "Tsukihime," frequently appears alongside his allies, such as Arcueid Brunestud and Ciel, as they navigate bizarre situations, including mundane tasks like running a café or participating in over-the-top competitions. Similarly, characters from "Fate/stay night," such as Saber, Rin Tohsaka, and Shirou Emiya, are featured in humorous skits that parody their original roles, such as Saber's obsession with food or Rin's tsundere tendencies.

The series also introduces original characters, such as the mischievous cat-like mascot Neco-Arc, who often serves as a chaotic force driving the humor. Recurring segments include the "Holy Grail Grand Prix," a chaotic race where characters compete for the Holy Grail using absurd vehicles and tactics, and "The Adventures of Neco-Arc," which follows the mascot's surreal and nonsensical escapades.

Interactions between characters from different franchises are a key highlight, with crossovers that play on their contrasting personalities and abilities. For instance, the series humorously explores the dynamics between Shiki and Shirou, or the rivalry between Arcueid and Saber. The humor often relies on exaggerated traits, fourth-wall breaks, and references to the source material, making it particularly enjoyable for fans familiar with Type-Moon's works.

While the series lacks a traditional overarching plot, its episodic nature allows for a wide variety of comedic scenarios, ranging from slapstick comedy to clever wordplay. The tone remains consistently light and absurd, with no serious stakes or dramatic developments, focusing instead on delivering quick, entertaining vignettes. "Carnival Phantasm" serves as a celebration of Type-Moon's characters and lore, reimagining them in a playful, comedic context that contrasts with the often serious tone of their original stories.