Teenager Girl

The teenager girl is a minor character in Train to Busan.

She is portrayed by Shim-Eun-Kyung.

History
Although she has a fairly minor role, she's the person who causes the outbreak on the train.

Seconds before the train departs, she staggers into the train without anyone noticing. She hides out inside a bathroom stall and reveals that she was bitten on the leg. She starts to freak out and used her stockings to tie her leg near the bite wound to possibly slow down the infection. Although it does slow down the infection a little she eventually passes out and dies. She is later discovered by a train attendant girl. The attendant calls for assistance through her radio but the teenager turns into a zombie as she is doing this and attacks her. Shortly after, she starts attacking other people and starts the zombie outbreak inside the train.

She is not seen for the rest of the movie but presumably died or escaped when the burning train crashed into a structure.

Trivia

 * She is also the voice actor of the female main character (Hye Sun) in the prequel "Seoul Station".