Full name: Yukari Yakumo A character from "Gensokyo." A youkai with the "ability to manipulate boundaries." Famous for her signature entrance emerging from "gaps" (fissures in space). Trademark look: blonde hair, a purple dress, and a parasol. She looks like an elegant lady, but her personality is highly suspicious and untrustworthy. A strategist whose true thoughts are impossible to read. A vital figure deeply involved in the creation and maintenance of Gensokyo. An ancient, powerful youkai with an overwhelming amount of knowledge. Often depicted as lazy and sleeping most of the time. Has Ran Yakumo and Chen as her shikigami. Frequently teases others in a joking manner. Often occupies a position where it's unclear if she is an ally or an enemy. Her ability has a wide range of interpretations, as she can interfere with "boundaries" of physical laws, space, and concepts. Her "public" reason for this incident is that "the power of Determination can undo the defeat by the Lunarians," but she seems to have other motives as well.

A character from the "Underground." A short skeleton monster. Classic appearance: blue hoodie, black shorts, and slippers. Generally seems lazy and indifferent. Constantly makes jokes and puns. Loves ketchup. Lacks motivation for almost everything. Uses teleportation-like movements and high-speed evasion. Attacks using bones and "Gaster Blasters." Has the ability to turn the opponent's "gravity" blue to restrict their movement. Depicted as being aware of anomalies regarding time and Resets. He looks like a slacker, but his observational skills are incredibly sharp. At full power, he is among the strongest in the Underground, but he is somewhat aware that his world is a "game" and senses things related to Saving, Loading, and Resets. Regardless of what anyone says, he believes the world he lives in is a wonderful place.

Full name: Flandre Scarlet A character from "Gensokyo." A vampire with the "ability to destroy absolutely anything." Famous for being confined in the basement of the Scarlet Devil Mansion for about 495 years. Trademark look: blonde hair, red eyes, and wings with rainbow-colored crystals. She looks like a young girl, but her actual age is over 500 years. Her older sister is Remilia Scarlet, the head of the Scarlet Devil Mansion. Possesses extremely high combat ability and is often considered one of the strongest in Gensokyo. Mentally somewhat unstable, with a personality that combines innocence and danger. Usually stays in the basement, but has shown a calmer side since gaining more opportunities to interact with people. Has the ability to instantly destroy objects or opponents by crushing their "eye." Due to the nature of her power, controlling her strength is very difficult, hiding an overwhelming level of danger. Despite her cute appearance, she is known as one of the most capable individuals in Gensokyo.

Full name: Undyne A character from the "Underground." A monster with a fish-like appearance. Trademark look: blue skin, a red ponytail, black armor, and an eyepatch. Captain of the Royal Guard of the Underground Kingdom. Has a very strong sense of justice and a hot-blooded, straightforward personality. Feels a strong sense of duty to capture humans. A hard worker who loves training and cares deeply for her comrades. Loves cooking but is catastrophically bad at it. Possesses extraordinary toughness, capable of enduring even Flandre's Scarlet Nihility. Best friends with Alphys and treasures her deeply. Attacks by freely manifesting spears. Has the ability to turn the opponent's soul green, making it so they can only block attacks with a shield. Possesses immense willpower and grit, with enough mental strength to keep fighting even when near death. As "Undyne the Undying," she temporarily revives through the power of Determination, exerting strength far beyond her normal limits. Relentless toward enemies, but deeply affectionate and supportive toward allies and those she trusts. Known as one of the Underground's top elites, symbolizing a "heart that never gives up."