« Ya Girl’s showing off a new costume. »

Girlfriend is a young woman with light skin and long, thick auburn hair. Two short locks of hair stick out of her head, one being much smaller than the other, and the shine on her hair resembles a skull. She wears a sleeveless red minidress and matching high heels. Her fingernails are painted red, as shown in her singing animations, where she points with both hands in the direction of the arrow note being hit, although sometimes this detail is not added. She normally sits with her legs crossed on a large gray speaker, with two smaller gray speakers laying beside the large one. She is drawn in a chibi style.

During Week 5, her sleeveless red minidress has a fluffy white collar, and she wears matching red gloves with white cuffs, white thigh-high stockings with small red bows, and yellow bell earrings. The speakers she sits on are all wrapped in festive Christmas lights with green wiring.

During Week 6, her regular appearance is brightened and rendered in a pixel art style. Her stereo has added shading and shine.

In the Ludum Dare prototype, she sits on a dark blue-magenta winners' podium resembling stairs. Girlfriend is portrayed as a young, mysterious woman. With a love for cherry soda and her boyfriend, she seems to be calm and collected in almost any situation, even in the face of death. Being a demon, she seemingly possesses a great deal of power, but she mostly chooses to hide it. She is always seen with Boyfriend at her side, courtesy of true love, as she genuinely loves him very much.

Like Boyfriend, Girlfriend lacks intelligence to the point of being unafraid of almost anything.[3] In general, she either does not realize when she is in danger or is confident that she can get out of such situations,[4] which may also be due in part to the power she has. Her lack of intelligence can result in her getting into difficult situations, such as getting her hand stuck in peanut butter jugs and having to wait for hours for someone to help get it out.[5] However, she is still capable of making smart decisions and knows what to do when dealing with taxes[6] and facing death.

Girlfriend has been diagnosed with ADHD and ASD.[7] The only individual she has been shown speaking to is Boyfriend. In Week 6 and Week 7, she does not speak at all, and she seems to barely acknowledge the opponent, if at all. Furthermore, she occasionally has poor object permanence.[8] Girlfriend's talents as an artist and painter show that she is a creative individual. She has a poor concept of time, too, which is a common ADHD trait. She doesn't know very well how to handle money, either; she will normally make commissions (due to being an artist), but she will ask for 1 trillion dollars,[9] or when she has to pay for a hamburger, she will pay less than what the hamburger costs.[10]

Girlfriend has been described as being mean "in her own special way."[11] She also likes to do immoral things, appearing to not care about the consequences of her actions as long as she gets what she wants. For instance, using her mother's limousine, she and Boyfriend hold up McDonald's drive-through slots as they hold the store hostage to get whatever food they want.[12] Girlfriend is afraid of thunder and lightning;[20] she will briefly react fearfully whenever they occur along with Boyfriend in an animation in Week 2. Girlfriend is nice and chunky, just like Boyfriend likes her.[46]

Girlfriend was stated to weigh 900lbs in a Tweet by ninjamuffin99.[2] However, Boyfriend has been officially depicted carrying Girlfriend with no difficulty in multiple instances; it remains to be seen how this is explained. If Sonic.exe ever tried to mess with Girlfriend and Boyfriend, he could trap them in a nightmare dimension for all eternity, but if he mentioned there's no McDonald's, they would immediately kill him and escape.[59] If there was a McDonald's, they would presumably stay