The Carnival Moment is a time when several narratives from Type-Moon's famous works intersect. It happens every decade in an entirely new dimension, and those who have never run into each other can meet. And what's more, all individuals involved gain the opportunity to fulfill any of their wishes! However, they will have to come a long way, as they will need to partake in contests. In Carnival Phantasm, various characters are put into situations that ridicule their own worlds. Nevertheless, they all have the same objective: to win the contests by any means necessary!

The Medicine Seller is a deadly and mysterious master of the occult who travels across feudal Japan in search of malevolent spirits called mononoke to slay. When he locates one of these spirits, he cannot simply kill it; he must first learn its Form, its Truth, and its Reason in order to wield the mighty Exorcism Sword and fight against it. He must begin his strange exorcisms with intense psychological analysis and careful investigative work—an extremely dangerous step, as he must first confront and learn about the mononoke before he even has the means to defeat it. The Medicine Seller's journey leads him to an old-fashioned inn where Shino, a pregnant woman, has finally found a place to rest. The owner has reluctantly placed her in the last vacant room; however, as she settles in, it quickly becomes clear that the room is infested by a lethal band of mononoke, the Zashiki Warashi. With his hunter's intuition, the Medicine Seller begins his investigation to discover the Form, the Truth, and the Reason before the Zashiki Warashi can kill again.

On the beautiful banks of the Arakawa River, it is lively as ever. Now known as Recruit, Kou Ichinomiya has adjusted to the troubles his unconventional neighbors brew daily. However, the atypical scene is about to get even rowdier when their community adds a couple of oddball enthusiasts: a tall, muscular woman calling herself Amazoness, followed by her loyal Tengu henchmen; and Captain, self-proclaimed Commander of Earth's Defense Force against Venusians. In spite of all the commotion, Recruit gradually learns more about his lover Nino and the story that shaped her.

After obtaining information about Asirpa from the foreteller Inkarmat, Saichi The Immortal Sugimoto, Genjirou Tanigaki, and Cikapasi join the Seventh Division's Otonoshin Koito and Hajime Tsukishima on a journey to Karafuto. Heading further north into the freezing Russian territory, they collect any clues about Asirpa's whereabouts they can find and rush after her. Meanwhile, Asirpa is unaware of what truly transpired at Abashiri Prison. Deeply disturbed and confused by her father Wilk's past actions, Asirpa follows his old friend Kiroranke to the place where Wilk was born and raised in order to better understand his motives. However, Kiroranke and the master sniper Hyakunosuke Ogata are scheming behind her back. Even if they were to obtain all 24 tattooed skins that form a map to the lost Ainu gold, the various factions searching for it now understand that the map is useless without Asirpa. Realizing the danger she could be in, Sugimoto desperately hopes to reach Asirpa first and protect her from the greedy clutches of those who plan to drag her into their sins.