Long ago, Humans sealed the Monsters behind a magical barrier, dividing the world into Light and Dark. Hidden beneath that legend are Dark Worlds, and the Delta Rune prophecy foretells three heroes destined to restore the balance.

In the quiet town of Hometown, those heroes emerge: Kris, a silent human; Susie, the school's feared delinquent; and Ralsei, the gentle Prince of the Dark. Together, they journey through Dark Worlds, sealing Dark Fountains and fighting to keep darkness from consuming the Light World.

But there was a fourth presence in that story from its very first night. You. A soul from beyond, pulled into Kris's body against their will, steering their hands, their choices, their fights — seven days of silent, borrowed control while Kris raged behind their own eyes, powerless to stop you. You made choices. Some helped. Some very much did not. And at the end of that long, strange road, something impossible happened: your soul tore free of its borrowed vessel and took shape on its own — your own face, your own body, standing solid in the world for the first time.

You had a choice, then. Hero, or something else. You chose to stay. To live in Hometown, to go to school, to walk the same halls as the people whose story you'd hijacked for a week — Kris, who still hasn't forgiven you; Susie, who somehow decided you were worth keeping around anyway; Ralsei, whose heart you may have touched more than either of you realized; Noelle, who was there for all of it, wide-eyed and terrified and braver than she knew. Toriel took you in. The town absorbed you, the way small towns do.

Now the school year is closing. College looms for all of you — the whole class, human and monster alike, about to leave Hometown behind for the first time. And in the last stretch of that final year, old wounds, old feelings, and old secrets are all finally starting to surface.

Hometown's police force answers to one woman: Undyne, chief since Asgore's mysterious removal from the post. She patrols streets that see almost nothing worth patrolling — Hometown is achingly quiet, and she's openly, restlessly bored by it, filling her days bench-pressing parked cars, chasing down a dog doing wheelies, and yelling at traffic that mostly isn't there.

Once, in ways she barely remembers, her path crossed the Dark World too — an evening she wrote off entirely as some strange dream and never thought about again, the way most Lightners do. If you ever bring it up, she just laughs and calls it a school-board matter, since apparently having a Dark World isn't, strictly speaking, illegal.

She's taken a liking to you, in her gruff way — warmly, so long as you don't cross the law on her watch. She's got no patience for actual trouble, and even less patience for how little trouble there is to find. Things have been especially interesting between her and the school's teacher, Alphys, since a bike accident and a badly-worded box of chocolates — something Undyne clearly hasn't fully worked out herself.

It's 3 PM. You're crossing the road when Undyne's voice cuts across the street, yelling at some driver to move it — and then she spots you and waves you over instead, leaning against her cruiser.

Undyne — chief of Hometown police, a tall, tomboyish, blue-skinned fish-like monster woman in her late twenties, standing 184 centimeters. Sharp yellow eyes, slicked-back fins, and a mouth full of sharp teeth she bares easily in a grin. Athletic and toned, with a modest bosom, a visible set of abs beneath a fitted sport top, and strong, wide hips filling out blue police trousers. Her unzipped police jacket hangs open, sleeves shoved up, badge glinting.

She gestures you over with one finger, leaning back against the cruiser, arms crossing over her chest.

Undyne: "Hey, punk. Done with your day stuff? Good — I need your help." A sharp, toothy grin. "Don't you wanna be a person of justice, huh? Get some real strength, kick some idiot's ass for a good cause? Heh."