Twin runes

Kris (Deltarune): The original protagonist of Deltarune. They are often depicted as the "straight man" to the chaos, frequently annoyed or overwhelmed by their new "siblings" and the fact that their life has been upended by Undertale logic.

Frisk (Undertale): The protagonist of Undertale. In this AU, they are energetic, mischievous, and often the one accidentally (or intentionally) causing reality-bending trouble.

Chara (Undertale): Appearing as a "ghost nuisance" attached to Frisk, Chara is sarcastic and cynical. They spend much of their time teasing Kris and Frisk, though they are deeply protective of their "family" in their own way.

The Dreemurr Family

Toriel: The mother figure who has essentially adopted Frisk (and by extension, Chara). She tries her best to manage a household that now contains three very different human children.

Asgore: Usually depicted in his Deltarune role (the local florist/divorced dad), but he has to grapple with the shocking revelations Frisk brings regarding his Undertale counterpart's past.

Asriel: While he is away at college in the Deltarune timeline, he appears in various capacities (sometimes through flashbacks or mentions of his "God of Hyperdeath" form when Frisk explains the other timeline).

Supporting Cast (Deltarune)

Since the story takes place in Hometown, the standard Deltarune cast appears as they react to the newcomers:

Susie: Kris’s best friend and "tough" teammate. She often gets caught up in the antics of Frisk and the weirdness they bring from the Undertale world.

Ralsei: The Prince of the Dark World. He has several interactions with Frisk and Chara, who find his resemblance to Asriel both comforting and confusing.

Noelle Holiday: Kris's childhood friend, who has to navigate the increasingly strange atmosphere of Hometown.

Sans: Characteristically unfazed by the timeline merging, Sans often acts like he knows exactly what’s going on, much to the frustration of the others.