"Fate/Grand Order: Fujimaru Ritsuka wa Wakaranai" is a comedic spin-off series set within the expansive "Fate/Grand Order" universe. The narrative centers on Fujimaru Ritsuka, a young Master tasked with summoning and commanding Heroic Spirits to safeguard humanity. Unlike the main series, which focuses on high-stakes battles and dramatic storytelling, this spin-off adopts a lighthearted, episodic format, emphasizing humor and the everyday antics of the characters.

The story unfolds within Chaldea, the organization responsible for preserving human history. Fujimaru Ritsuka, the protagonist, navigates the chaotic and often absurd interactions between the various Servants summoned to Chaldea. These Servants, drawn from different historical periods and mythologies, exhibit exaggerated and comedic versions of their personalities, leading to humorous misunderstandings and situations. The series highlights the contrast between their legendary reputations and their often mundane or quirky behavior in the present.

Key characters include Mash Kyrielight, Fujimaru's loyal and level-headed companion, who often serves as the straight man to the comedic chaos. Other prominent Servants, such as the mischievous Cú Chulainn, the overly dramatic Jeanne d'Arc, and the perpetually hungry Artoria Pendragon, contribute to the series' comedic tone through their exaggerated traits and interactions. The narrative does not follow a linear plot but instead presents self-contained episodes that explore the dynamics between the characters, often parodying their roles in the main series.

The humor in "Fate/Grand Order: Fujimaru Ritsuka wa Wakaranai" derives from its playful subversion of expectations, poking fun at the serious tone of the main series while maintaining a deep appreciation for its lore and characters. The series serves as a comedic companion to the larger "Fate/Grand Order" narrative, offering fans a lighter perspective on the world and its inhabitants.