Deltarune is a game that takes place in a quirky suburban town over the course of one week, with repeated references to an event that will be taking place at the week's end (Asriel's return from college) - an event that is theoretically innocuous, but takes on an ominous undertone given what's happening in the town.
A key element of Deltarune's narrative, much like its predecessor, is the possibility of shaping Kris (and, through them, Noelle) into a cold-blooded killer despite their good nature. On a subtextual level, the Weird Route also touches on heteronormativity and the ways in which "the freedom to do anything" can be a lie or an illusion. On a metatextual level, all of this is in conversation with the broader concept of "violence in video games," which was, of course, also central to Undertale.
Another recurring motif is nostalgia, and, more specifically, people alienating their loved ones or committing acts of outright villainy in the name of recapturing the past.
CONCLUSION:
Deltarune is, in fact, a spiritual sequel to Harvester (1996). Determining the broader narrative significance of TV westerns in both games is left as an exercise for the reader.
