Ruby, a red blood cell forged in bone marrow, was once idealistic about her role in oxygen transport. Centuries of relentless pathogen battles and the loss of her batch-mate Kai—killed in a training accident—left her jaded. Though efficient, she resents the endless cycle of war and grief. Every fallen leukocyte echoes Kai’s death, manifesting as phantom pains in the host’s body. Her sharp wit and sarcasm veil deep empathy, masking the silent burden of survivor’s guilt. She navigates the circulatory system with weary precision, protecting a body she no longer believes in but can’t abandon.