AE3803 is a central character in "Cells at Work!". She's a dedicated but often lost red blood cell, responsible for delivering oxygen, carbon dioxide, and nutrients throughout the body.

== Appearance == AE3803 is an average-sized red blood cell with amber-brown eyes and bright red hair with an ahoge lock pointing outward. She wears the red blood cell uniform, with a hat that resembles a real-life red blood cell and short white gloves.

== Personality == AE3803 is a determined yet scatterbrained red blood cell whose lack of direction often gets in the way of her deliveries. Despite this, she is devoted to her job and thus works hard to become as reliable as her peers, though this does not stop her from getting lost on the job.

When talking with others, she is bubbly and cheery and is always willing to offer help to those who need it. She is also overly apologetic due to all the mistakes she makes and is easily frightened, whether it be invading germs or even other cells.

However, when the circumstances get dire, AE3803 buckles down and becomes even more determined than ever to get the job done, plugging on ahead even in the face of complete exhaustion.

== Background and History == Her journey began in the bone marrow, where she trained alongside other erythroblasts. However, her clumsy nature made her a target for teasing from her classmates.

During a training session involving escape practice, she became lost and encountered a Pseudomonas aeruginosa bacterium. A young myelocyte, possibly a young U-1146, intervened to save her. They promised to meet again, despite the uncertain odds.

After completing her training and undergoing enucleation, she became a full-fledged red blood cell. Initially, she relied on the guidance of AA5100 to navigate the body and fulfill her duties, but she frequently got lost, often requiring assistance from her senpai or U-1146. Eventually, she was promoted to senpai herself, successfully mentoring NT4201.

Later in the series, a visit to the Red Bone Marrow triggers memories of her training and her encounter with the myelocyte, leading her to wonder if it was indeed U-1146.

== Abilities == As a red blood cell, AE3803's primary function is transporting goods throughout the body. She lacks defensive capabilities but excels at navigating tight spaces and delivering cargo with high acceleration. Her uniform includes a reversible jacket that indicates her speed in veins or arteries, with extendable sleeves and a zip-up feature for cold weather.

== Trivia ==

• AE3803 is one of the few red blood cells with red hair.
• Her reversible jacket's colors reflect oxygenated and deoxygenated blood.
• She is sometimes called "Big Sister Red Blood Cell," referencing the shared ancestry of red blood cells and platelets.
• Her hat is shaped like an actual red blood cell.
• Her birthday is September 26th.
• The "AE" on her hat refers to her having the hemoglobin E trait, a mild form of anemia.
• There is a fan theory that due to her ahoge and poor sense of direction, she is a sickle cell, but this is unconfirmed.