Demon Realm
On Halloween 2019, a “few hours” after the end of the crisis caused by his malfunctioning Spirit Realm Gateway, the Crew of the Copper-Colored Cupids' resident Mad Scientist Frankenstein-818 unveiled his newest invention, a gateway to the Demon Realm, which reaped “rather mixed reactions from the Cupids”. (PROSE: The Ghosts and the Machine)
Behind the scenes
The Demon Realm was used as the name of the main fantasy universe of The Owl House, a fantasy animated series which debuted on January 10th, 2020, around two months after the release of PROSE: The Ghosts and the Machine (October 31st, 2019) — although the name was first used in the series in its sixth episode, Hooty's Moving Hassle, which aired on February 21st. Although press release as early as February 2018 had referred to the show's setting as “the Demon Realm”, by Lupan Evezan's own account, the name-drop was a coincidence.
In hindsight, however, and despite the reference to a copyrighted concept in so many words (unusual in The Crew of the Copper-Colored Cupids), it is likely that the Demon Realm referenced in the story should be understood as retroactively being the same dimension documented in The Owl House. The Prime Universe of the Cupids series is well-established to be synonymous with the Disney comics universe — which was shown to have multiversal interactions with the Owl House Demon Realm on several occasions, more or less indirectly, such as in the YouTube short Scratch Haunts, where a singular character, the ghost Scratch, visited Duckburg, Amphibia (from the eponymous series) and the Demon Realm in quick succession. This makes it likely that a “Demon Realm” mentioned by the Cupids, who ultimately originated in the Prime Universe, would be this one.
If taken seriously, this notion would add a layer of dramatic irony to the Cupids' lack of interest in the gateway, as much of the plot of The Owl House would go on to feature characters vying for access to a very limited number of portals between the Demon Realm and other worlds including human protagonist Luz's native Earth.
