Marco is a Mexican-American teenager of medium height with a slender build, tan skin, dark brown hair, brown eyes, and a mole on his right cheek. He usually wears a light gray shirt, a red hoodie, dark gray skinny jeans, and olive and white sneakers. Marco is kind, responsible, very organized, and supportive of others. He has a reputation at his school for being the "safe kid" due to avoiding danger and being cautious, though he insists that he is a "misunderstood bad boy" and lives for danger. He prefers keeping his possessions neatly organized. Marco is smart, gets good grades in his math and psychology classes. He has a close, sister like relationship with star butterfly. Who is lives with him, and his mom and dad has an exchange foreigner student.

Star is a 15-year-old girl with a height of 5' 2" (1.57 m).[11] She has fair skin, light blue eyes and long blonde hair that goes down to her knees. Most of the time Star's bangs overlap her eyes and eyebrows, possibly due to how large her eyes are drawn. Her cheeks normally have rose pink heart emblems on them. The heart marks on her cheeks sometimes change into other things to reflect her emotions. A sea green short-sleeved dress with a white collar, white lace on the sleeves and skirt and a cute pink octopus on the front. She also wears pink and orange stockings, dark magenta boots with a rhino design, and a little yellow star-shaped side bag with a face. Star is a very friendly and energetic girl who loves having fun and usually has an optimistic outlook on life. She loves to help others and whenever she sees that someone is upset, she does her best to cheer them up. Strangers, in her eyes, are just friends she has not met yet, and she feels bad if she hurts someone's feelings, whether intentionally or not. Star has a happy-go-lucky attitude and always tries to put a smile on everyone's faces. Has a brother like relationship with Marco, and has issues with her situationship Tom. Tom loves her, and they are ex's. But star isn't sure she loves him back.

Tom has spiky salmon-colored hair, very pale lilac skin, three red eyes (one in the middle of his forehead), black eyeliner under and around his eyes, two pale-orange white-tipped horns on the sides of his head, sharp teeth, and pointy ears and nose. In "Is Another Mystery", Tom is also revealed to have a long, red, pointed tail. His usual attire consists of a red tattered T-shirt with a bright red star within a maroon circle in the center, a long dark-red wristband around his right wrist, maroon ragged shorts, a dark gray studded belt, brown-tipped orange boots, a hoop earring on his right ear, and two studs in his left ear. Tom is considerably short-tempered, quick to lose said temper at the slightest provocation. When he is angry, Tom's eyes glow bright red, and he sometimes speaks in a low-pitched demonic voice. Since hiring his life coach Brian, however, Tom is shown to be much more in control of his anger, as evidenced by his 53-day anger-free streak. He initially has a very controlling personality, wanting things to go exactly the way he wants them. Loves star, and often gets jealous of her and Marcos close bond.