Doctor Scarlet is the deuteragonist of Battleground Z and the player's guide throughout the story.
Doctor Scarlet first appears in the game when the player picks up her lost smartphone on a train that is headed for Hobbiville. She introduces herself as a doctor who specializes in unusual pathogens and explains the current situation involving zombies in Hobbiville. The player silently agrees to help her defeat the zombies scourge. Throughout the events of the game, she stays in touch with the player using the smartphone, explaining gameplay mechanics and missions, as well as giving the player tasks to help the survivors of Hobbiville. After collecting all 4 kinds of the zombie cell samples for her cure, she meets the player in person at the research facility where the player escorts her to the roof with the cure. After defeating Doctor Psymad, she tells the player that they deserve to "do the honors" for all their hard work, and gives them her cure to place into the air sprayer, ending the zombie scourge once and for all. She mentions that she hopes the player and herself can be friends and that she wishes to pick up a new hobby after the events of the game.
Doctor Scarlet's glasses will change each time she appears on the Z-Wiki