Neco-Arc, a Neco Spirit, morphs into Mysterious Neco X in Fate/Grand Carnival, mimicking Mysterious Heroine X/Artoria Pendragon. This change is a humorous element in the series. Neco-Arc and other Neco Spirits operate Ahnenerbe, a coffee shop where worlds merge every decade. The transformation into Mysterious Neco X forms part of the introductory skits of each episode.