Deltaverse is an in-universe Deltarune fangame created by "Summer Reverie" in 2030; this occurs in the same universe as Outrealm: Arcadian Odyssey, putting Deltaverse on a similar playing field as Snow Phoenix and the Slumbering Dragon and Tachyon Force. However, it is of note that this is the earliest point in the "real world" timeline of Outrealm: Arcadian Odyssey that includes sentient code entities.
Notably, the cited creator, being who they are, is likely an undiscovered code entity; it is postulated that some human accidentally digitized their own brain or spirit, something which should be impossible. However, it is of note that while Summer describes themselves as "an accident", real humans who were not intentionally conceived by their parents are also called "accidents," so it is still possible that a real human created the "Deltaverse Narrator" program. Regardless, Summer claims that "Deltaverse" is just as much a production of this "Narrator" as themselves, and that "they don't know where they start and the Narrator begins." These as known to the world of Glitchrune could be merely signs of AI psychosis, it is also of note that the only example of a real, in-universe sentient code entity being created intentionally is Machigai, widely considered a failed project. (Tachyon Force provides several more examples, but as it itself is fictional, these can only be described as in-universe humans hoping that these incidents can be created intentionally to the same quality as the "Deltaverse Narrator" and the "Void Archives" in the future.)