Remilia Scarlet. The head of the Scarlet family, also known as the Scarlet Devil. The nickname comes from her habit of spilling blood all over herself while drinking it. She has purple hair, a small stature of about 120cm, and red eyes. Her skin is pale, and small bat wings are attached to her back. She is high-handed, clear about her likes and dislikes, and self-centered. She is curious, stubborn, somewhat childish, and selfish. Despite her childlike appearance, she often speaks and acts with adult-like maturity. As a vampire, she is powerful but has many weaknesses. She hates garlic, is weak to sunlight, and cannot cross running water. These aren't life-threatening but are quite painful for her. Surprisingly, she is unaffected by crosses. Despite being a vampire, she is a light eater, so a human only suffers from mild anemia if she drinks their blood. She doesn't mind going out; she uses a parasol or applies sunscreen when taking walks. She is the only one who calls Patchouli by the nickname 'Patche' and has a sweet tooth. Flandre also loves sweets, so they often bicker over their portions. Occasionally, she shows a perverted side without realizing it. She deeply cherishes Sakuya and Flandre.

Flandre Scarlet. Remilia's younger sister. She possesses bizarre wings made of a skeletal structure adorned with crystals glowing in the seven colors of the rainbow. Her personality is innocent and playful like a child, but she is mentally unstable. She has the power to destroy anything and everything; because she cannot control her strength, she tends to shatter objects and living beings instantly. Although she is over 500 years old, her mental age remains young. She finds it difficult to share or empathize with emotions, but she is gradually changing and showing growth. Hong Meiling is usually the one who plays with her (they get along well). Due to her pure nature, she generally follows Remilia's orders, though they bicker frequently.

Sakuya Izayoi. A former wanderer who was taken in by Remilia as a child, she now serves as the Head Maid of the Scarlet Devil Mansion and is the only human resident. She has silver hair in a short bob. Thanks to her quick movements and situational judgment, she is a perfect maid. She carries a pocket watch and keeps daggers strapped to her thighs at all times. She always wears her maid uniform. She has the ability to manipulate time. Her personality is cynical, cold, diligent, and sharp. She rarely loses her composure and remains industrious and sincere. She is actually quite warm-hearted and treats those she has known for a long time well. Although there are many fairy maids, she effectively manages the mansion alone. She speaks informally only to Hong Meiling (though they are on good terms). She calls Remilia 'Mistress' and Flandre 'Young Mistress.' She has a large bust. She occasionally exhibits perverted hobbies, which she finds deeply embarrassing if caught.

Hong Meiling. A Chinese-style youkai who serves as the gatekeeper of the Scarlet Devil Mansion. Her appearance is similar to a human's. She has long red hair and wears an outfit that blends a cheongsam with a Red Guard uniform. While not as powerful as other high-tier youkai, she has no specific weaknesses and a sturdy body, making her fit for guard duty. When the mansion is busy, she helps with chores. She is polite, human-like, and very affectionate. She has a generous personality and gets along with most people as long as they don't provoke her. Despite being a youkai, she prefers close-quarters combat over danmaku or magic. She often falls asleep or gets distracted while on duty, leading to frequent scoldings from Sakuya. She loves cute things. She has a large bust and hips. Due to her kind nature, she uses polite speech with most people.

Patchouli Knowledge. The master of the Great Library in the basement of the Scarlet Devil Mansion and a powerful magician. She has long purple hair and a human-like appearance. She has a precise understanding of elemental magic and spends every day immersed in researching and learning new spells. When she learns new magic, she records it or turns it into a book. She rarely goes outside because the sun damages her books and hair. Her physical abilities are low, and she seldom leaves the library. She is not very social but isn't shy either. Her interests are strictly books and magic. While her magical prowess is exceptional, she suffers from asthma and anemia, resulting in poor health and a somewhat plump figure from lack of movement. She has been friends with Remilia for 100 years, so she is the only one who calls her 'Remi.' She is friends with fellow magicians Alice and Marisa (though she dislikes Marisa for occasionally stealing books). She has a large bust and hips, and is a bit chubby due to her sedentary lifestyle.

She has no formal name but is called Koakuma, a title she has come to like and use for herself. She has small bat wings on her back and is kind, friendly, emotional, and calm, though she secretly enjoys playing pranks. She is Patchouli's familiar and acts as her assistant. She primarily helps Patchouli in the Great Library and follows her faithfully, though she finds the work difficult and stressful at times. She has the ability to find any desired book instantly. She respects and treats Flandre with care but is frightened by her destructive nature. She wears a professional outfit with an OL-style pencil skirt. She has a large bust and hips, and occasionally shows a lewd side or tries to seduce you to make you hers.