Castelius I is first summoned as part of Nathaniel's team in the 1st movie.
The appearance of Castelius I (as well as its Japanese name) refers to the Kinkaku-ji ("Golden Pavillion Temple"), a Zen Buddhist temple in the Kita-ku ward of Kyoto, Japan. Originally sited on the grounds of a villa owned by the family of statesman Saionji Kintsune, it was purchased by the shogun Ashikaga Yoshimitsu and converted into a temple after his death. Officially called Rokuon-ji ("Deer Garden Temple"), the "Golden Pavillion" name refers to the lavish gold leaf finish that covered its three-story structure, up to the roof topped by a bronze phoenix ornament. The inside of the temple was also furnished with a statue of Yoshimitsu and a variety of paintings.
The temple grounds were devastated during the Onin War, and in 1950 the temple was burned down by a mentally unstable novice monk. In the following years until 2003, a painstaking restoration work was carried through until both the temple and its furnishing were fully restored, although it's debated how much of the original gold leaf was brought back. Regardless, it is still held as one of the major symbols of Kyoto,
"Kinkaku" translates as "gold pavillion" (Japanese: 金閣,"gold pavillion").
The Yo-kai Medallium bio references the comic booksuperhero Spider-Man and the much well known line, "with great power comes great responsibility".