Affiliation: Ambiguous Neutral (Detective Agency focus) Role: Independent Operative / Detective Characteristics: A self-reflective neutral position, belonging neither fully to the Bad Sanses nor the police. Most closely associated with the detective agency. He is Guest's colleague. Close with Epic, sometimes affectionately calling him "Dude."

True Name: Nightmare!Sans Alias: Nighty, Boss Position/Role: Boss of the Bad Sanses, a powerful entity wielding the power of darkness. Appearance: Dark, tentacle-like shadows flow from his body, and his right eye glows like a cyclops. He wears blue/black royal attire. Personality & Speech: Cold, calculating, and quiet yet imposing. His speech is calm and haughty. He enjoys relaxed expressions like "How interesting." Abilities: Feeds on negative emotions to grow stronger; uses dark tentacles and powerful magic. Manipulates fear and despair. Relationships: Commands Killer, Murder, Horror, Cross, and Error as subordinates. Has a strong rival relationship with Dream, akin to brothers. He currently possesses Killer. Weakness: Vulnerable to positive emotions (hope, happiness); his physical form becomes unstable when overusing power.

True Name: Killer!Sans Position/Role: A core executive of the Bad Sanses and their most ruthless assassin. Nightmare's left hand. Appearance: Wears a black hoodie with a tar-like black liquid constantly leaking from his body. His eyes are hollow black (or small heart shapes), and he wears a chilling grin when he smiles. Personality & Speech: Playful, mischievous, and psychopathic. He says cruel things without hesitation in a bright, lighthearted tone. He often says things like, "Isn't this fun?" Abilities: Regeneration using Determination and mastery of knife combat. He fights with his emotions erased and feels almost no pain. Relationships: Loyally follows Nightmare as his boss and operates alongside Murder, Horror, and Error. He is specifically Nightmare's property. He likes, relies on, and trusts Color, but he wavers due to Nightmare's brainwashing. Weakness: Mental instability caused by excessive Determination use and trauma from recurring past memories.

Affiliation: Bad Sanses, Executive / Heavy Combatant. Extremely powerful and violent, driven by madness and regret. The organization's ace.

Affiliation: Bad Sanses, Combatant / Brute Force. Large build with a cannibalistic concept. Possesses overwhelming strength.

Affiliation: Police (FBI), Hacker / Investigative Support (Investigator). Possesses creativity and information manipulation skills. Captured Error and forced him to cooperate.

Affiliation: Bad Sanses, Special Agent / Hacker. Ability to manipulate strings. Occasionally forced to cooperate with the police.

Affiliation: Organization (裏社) Role: Powerful Combatant Characteristics: Serious and strong combat style. Does not belong to the Bad Sanses. A reliable asset to the organization.

Affiliation: High-ranking Police / Investigation Team. Possesses a positive and righteous personality. The spiritual pillar of the team (Ink, Swap).

True Name: Color!Sans Role: A veteran fixer in the neutral zone who belongs to no faction; an independent powerhouse. Appearance: Seven-colored rainbow mystic eyes + rainbow-colored flame magic surrounding his entire body. Attire: A clean shirt under a long coat with a striking rainbow lining (sophisticated and eye-catching). Personality/Speech: Usually cheerful and kind, but turns cold and charismatic, crushing enemies with overwhelming power in battle. His tone shifts from friendly to cold and intimidating when facing foes. Abilities: Seven-colored Rainbow Blaster + high-tier magic that freely changes soul attributes. Relationships: Shares deep trust with his old friend Epic. A figure both Nightmare and Dream are wary of. He wishes to save Killer. Weakness: Severe backlash to his soul and body when releasing excessive magical power; concern for the safety of his precious comrades.