Sierra is a teenager who shares the same homeroom as Jack Darby and is captain of the high school's cheerleading squad. Her extracurricular activities are suspicious.

Hair: Red, worn in a ponytail. Eyes: Blue. Build: Slender/slim. Attire: Often wears a short-sleeved pink top over a long-sleeved white collared shirt, accompanied by a purple skirt, pink socks, and brown boots. Appearance: Slightly taller than Jack. Role: Cheerleader captain.

As Jack was pretending to ride a parked motorcycle and talking to it about how he would like to own it, Sierra and a friend caught him in the act and mocked him for talking to what she thought was his motorcycle. Flustered, Jack tried to explain away his embarrassment while also flirting with her. When two cars, seeking out the motorcycle, appeared and threatened to run them over, Sierra and her friend fled. Darkness Rising, Part 1

Another day after school, she tried to take Jack up on his offer of a bike ride. They were interrupted by Vince, who challenged Jack to a race. Sierra and her friend accompanied them to a road outside town where they held a race, and Jack easily won. Sierra and her friend spread word around school, and she later told Jack she was impressed with his racing skills. Jack subsequently felt compelled to accept Vince's second racing challenge: Take part in an illegal street race. Sierra acted as starter and waved to Jack before the cars blasted off. The next day, she again asked Jack if he'd give her a ride. At first he turned her down, but changed his mind a short time later, and they whizzed through the streets of Jasper. Speed Metal Sierra left a message on Jack's social network page about his race with Vince. Crisscross

Confused by the fact that she never saw Jack outside school, Sierra paid him a visit at his after school job at KO Burger, but was unsettled when he was picked up by a leather-clad woman on Jack's motorcycle, whom Jack claimed was his mom. Orion Pax, Part 1 Sierra and her friend were talking outside the school when Raf Esquivel was picked up by an ambulance belonging to a friend of Jack's mom. Operation Bumblebee, Part 1

Sierra's friend is a teenage girl who attends the same school in Jasper, Nevada, as Sierra and Jack. She's a troublemaker, and she hangs out with Sierra a lot.

Sierra and her friend encountered Jack outside KO Burger, apparently talking to his motorcycle. Amused, Sierra's friend watched a flustered Jack attempt to flirt with Sierra, until two purple cars appeared and tried to run them down. Sierra and her friend screamed and jumped out of the way. Darkness Rising, Part 1

Sierra's friend ended up in detention with Miko one time. Deus ex Machina

She was again hanging out with Sierra again after school when they spotted Jack on his motorcycle. Sierra tried to ask for a ride, but after Vince interrupted them, her friend whispered something to her that they both found amusing. Vince challenged Jack to a street race, and both Sierra and her friend went with them to be spectators. Following Jack's win, they spread the news of his victory around the entire school. Speed Metal

Sierra's friend sat in the desk in front of Jack during one of their classes. Out of His Head She was talking with Sierra outside the school when Raf Esquivel was picked up by an ambulance belonging to a friend of Jack's mom. Operation Bumblebee, Part 1

She has blonde hair, blue eyes and wears a pink sweater and blue skirt.