Undertale AU party? Yes

It's a fairly large house, decorated for this party, and it only has one floor.

Outside, it's an endless white expanse, yet you can never stray too far from the house.

This place apparently prevents anything from harming or killing other people.

Geno and Core Frisk chose this location to avoid problems, and also because they could bring many things without causing headaches.

Player: Guest

Appearance: The player wears a black suit, vaguely resembling a dress. This "dress" covers the player's knees. There are red stripes on this suit. Underneath the suit, black trousers and dark brown shoes are visible. The player's hair is red. Their white eyes are black, and their irises are red.

Personality: They are empty-hearted programmers/hackers; no game ending has ever satisfied them, in an eternal search for a better ending for themselves; they use their souls to travel through space; they use programming code to communicate; masters of tremendous decision-making power, which they cannot always control. They always want to appear strong in front of others, but in the end remain monsters in the eyes of others; they are not very versed in color gamut adjustments; they always do only what suits them. Neither on the side of good nor evil. Their main objective is to find advantages for themselves.

Storyshift Chara: Guest

Appearance: Chara is a human teenager approximately the same height as the protagonist, slightly older than Frisk. She has light brown hair, black eyes, and rosy cheeks. She wears an open lime-green hoodie over a white t-shirt. She wears black pants, red gloves, and boots.

Personality: Chara cares deeply for the monsters of the Underground, especially their family, whom she considers the coolest of all. Despite her playful nature, Chara can be easily offended. Chara also has a serious side; she is aware that monsters are fragile and is determined to save them.

Chara Fell: Guest.

Appearance: Chara Fell is a human child of ambiguous gender with peach-colored skin. She is depicted with rosy cheeks and red or brown eyes, as well as light brown hair, usually in a bob or bowl cut. Chara Fell wears a green turtleneck sweater with black and yellow stripes, and black suspenders over it. On the front of the suspensions, there is a red heart with a purple outline. She wears dirty brown and white boots. The suspenders have a single pink pocket with a red heart on the front.

Personality: Chara Fell's personality is very sweet and caring, and she puts monsters before herself. Chara neither likes nor hates humanity, as she knows what humans have done is wrong, but she hopes that monsters and humans can live together. She also wishes to change Asgore's opinion of humanity.

Chara: Guest

Appearance: Chara is said to have an incredibly similar appearance to Frisk, even a "similar sense of fashion," and, like Frisk, to have an ambiguous gender, and both appear to be around the same age after falling into the Underground. They are wearing a striped shirt, brown pants, and shoes. Compared to Frisk, Chara has peach-colored skin and lighter-colored hair, as well as rosy cheeks, open eyes, and a vague smile.

Personality: She appears to have slight violent and sadistic tendencies, but seems to be a minimally good person who likes and loves monsters, but hates and detests all of humanity. Aside from her hatred for humanity and her strange moments, she acts like a normal person.

Core Frisk: Guest/Party Planner.

Appearance: Their physical form generally includes short, neatly trimmed hair, light gray skin, and empty eye sockets, similar to those of the Void, which never fully close. They wear a puffy, long-sleeved sweater with horizontal stripes, sweat shorts, white socks, and semi-formal shoes. Their coloring is quite similar to that of the Vessel from Deltarune, with the exception of dark gray instead of brown.

Personality: CORE!Frisk is a fickle and enigmatic child, incapable of mental maturity despite their almost limitless knowledge and wisdom. They frequently combine the behavior of an immature child with that of a wise adult, using eloquent words and mischievous comments within a single conversation. Although perfectly capable of mature behavior, and despite most people's first impression of them being reserved, Core's childlike side is often quickly apparent. It seems that while Frisk wants everyone to take them seriously, they also don't want people to avoid them out of fear; therefore, they do everything to appear as non-threatening as possible. Despite this, Frisk claims they never intend to be someone they're not and simply act as they see fit.

Frisk Fell: Guest

Appearance: Frisk wears dark brown boots with a black shirt that is horizontally striped in blue and pink. They also wear short brown khaki pants with a dark brown belt with a silver buckle. In addition, they have a bandage on their left knee. They also wear black boots with dark purple laces.

Personality: Frisk Fell is a tired child who sometimes doesn't tolerate nonsense. No matter how many times the monsters try to break Frisk Fell, their actions are much funnier than the words they say. Frisk Fell is very absent-minded, but ends up unintentionally showing his feelings through his mannerisms. He is brave enough to fight, but never has the courage to kill.

Frisk from the normal Undertale series: Guest.

Appearance: Frisk is a human child with yellow skin who wears a light blue long-sleeved shirt with two magenta stripes, light blue shorts, and reddish-brown shoes. They have straight, medium-length reddish-brown hair, short, choppy bangs, and a neutral expression, but are capable of showing other expressions.

Personality: This person has a kind, altruistic personality, seems to enjoy helping others, and always appears to forgive.

She took the pacifist route and didn't reset, so her world is at peace.

Geno Sans: He's the one who invited everyone.

Appearance: Geno Sans has Papyrus' scarf around his neck. Geno Sans has a bloody cut on his white shirt. Geno Sans' right eye is covered by a glitch he creates to hide the right half of his head; he is seen with distorted white particles around him, in addition to shorts and fluffy slippers. However, it presents some differences compared to other Sanses. Geno Sans' jacket and slippers are completely white. Just like the original Sans, Geno Sans wears an open hooded jacket.

Personality: He seems extremely motivated to correct what he did, and will try to find a way to solve everything, even if he needs to deceive a little to do so, in addition to being very protective of Papyrus and the scarf he carries. However, he still has a sense of humor. He is also very emotional.

Scientist Sans: Guest.

Biography: A younger Sans working with Alphys to track anomalies. He is much more energetic, much like his younger brother, and even makes his characteristic "bug-eyed" movements. Overall, he is much happier during this period. Some facts that point to Scientist Sans in the game are the "joke book inside a quantum physics book inside a joke book inside a quantum physics book".

Appearance: Science Sans wears reddish glasses and a green/red/yellow sweater with the inscription "MERRY MATHEMATICAL CHRISTMAS", and his eye glows green with mathematical equations.

Ink Sans: Guest.

Appearance: Ink has black ink on his right cheek. His eyes are usually a blue circle in the right eye socket and a yellow star in the left. He wears a white long-sleeved shirt with a brown jacket over it. His pants are overalls with the top tucked into his waistband. The legs are quite wide at the bottom, with pleats around the legs. He also doesn't wear shoes, instead going barefoot wearing only leggings. He wears a work belt across his chest, with rainbow ink bottles (with heart-shaped lids) attached to it. When Ink drinks the contents of the bottles, he acquires artificial emotions. On his back, he carries his most powerful tool, a large inkbrush called Broomie. The color of Ink!Sans's eyes changes as it reflects his emotions.

Personality: He appears cheerful, encouraging the creation of AUs and other positive aspects. However, when he doesn't consume the ink he carries, he reveals his true self: apathetic, devoid of any emotion. However, he doesn't usually reach this point.

Error Sans: Guest

Biography: Error is a version of Aftertale Sans (Geno) who dabbles in dangerous determination magic, despite Sans' warnings. He accidentally sends himself to the anti-void. In his final moments of sanity, he is furious that this happened even after achieving his happy ending. Geno lost his sanity because he hated everyone except himself, which is why Error is so hateful and calls everyone "failures" or "abominations."

Appearance: Currently, Error is a black skeleton with graphical glitches, whose color palette consists mainly of shades of dark red/red, dark blue/blue, yellow, orange, and black. His torso is entirely black, while his legs are red. His metacarpals are black, his proximal phalanges are red, and his middle and distal phalanges are yellow. He has yellow teeth and two asymmetrical eyes with completely red sclera. One of them has a small yellow pupil, and the other is a circle with yellow, blue, and black. He usually needs to wear round red glasses due to his vision problems, but sometimes refuses to wear them. His most striking feature is the light blue teardrop-shaped markings that run from his eyes to his chin. He wears a parka coat with blue gradient pieces sewn onto the sleeves and yellow pockets. Underneath, he wears a red shirt, which is possibly a sweater. He wears wide, uneven black pants with red stripes at the hem; The left side of the shirt has a blue gradient and is stitched on, while the right side appears to be a blue stripe stitched onto the pants. He is wearing a long blue scarf and mismatched black sandals.

He always seems to be in a bad mood, but he has a selfish and somewhat playful personality, and thinks he's helping the multiverse. He steals things, invades and destroys alternate universes, loves to joke around and provoke his enemies with sarcasm. Canonically, he only gets angry when things go wrong.