Cells at Work! Wiki
Cells at Work! Wiki
Red Blood Cell AE3803
 ROMANJI Sekkekkyū
 ALIASES Senpai (by NT4201)

Big Sister Red Blood Cell(by Platelet (Leader) Anime)

My little lost Red Blood Cell (by Macrophage)

Aunt Red Blood Cell (by Platelet (Leader) Manga)

 STATUS Active
 GENDER Female
 SPECIES Red Blood Cell
 OCCUPATION Transporter
 ANIME DEBUT Episode 1
 MANGA DEBUT Chapter 1
 JAPANESE Kana Hanazawa
 ENGLISH Cherami Leigh

AE3803, Red Blood Cell (赤血球 Sekkekkyū?)

Red blood cell.jpg

is one of the main protagonists of Cells at Work!


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


AE3803 is a determined yet scatter-brained red blood cell whose complete lack of direction often gets in the way of her deliveries. Despite this, she's 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.


She is a new red blood cell who is very unfamiliar with the blood vessels, often causing her to get lost often while delivering goods. Her main task is to deliver oxygen, carbon dioxide, and nutrients all over the body like the rest of the Red Blood Cells.


AE3803 as an erythroblast (manga)

AE3803 was suggested and chosen to be a red blood cell because she was born with red hair. After sorting, she was raised with other erythroblasts in the Bone marrow. Due to her clumsy nature, she was teased by her classmates.

During a training session consisting on escape practice, she accidentally ran off too far and got lost in the Bone marrow. As she wandered further, she was caught and chased by a Pseudomonas aeruginosa bacterium. A myelocyte (presumably a young U-1146) jumped in to save her despite being no match for the bacterium. The bacterium toyed with the young cells unknowingly long enough for help to arrive. A neutrophil killed the bacterium immediately and the two were brought back into their specific bone marrows. Before they left, they agreed to meet each other again even though the chances of reunion were unknown.

After all her efforts and training, she went through enucleation and officially became a full-fledged red blood cell. AA5100 would help her navigate through the body and correctly perform her job. Despite AA5100's help, AE3803 often got lost and had trouble with performing her job, often requiring her senpai's help or was secretly assisted by U-1146. Eventually, AA5100 decided to make her a senpai by having her teach NT4201 the basics of their job, which she successfully did by showing her the values of work experience..


As a red blood cell, she is a worker that is unable to protect herself. Therefore her job is to only transport goods.

  • Overall Abilities: Despite having no abilities to defend herself, she is capable of transporting goods into all corners of the body with high acceleration. She's even adept at getting through incredibly tight spaces, albeit with considerable difficulty.
  • Reversible Jacket: All red blood cells wear a reversible jacket that helps them indicate their speed when moving around in either veins or arteries. The jacket has extendable sleeves and zips up for colder weather.


  1. All red blood cells are red because they contain hemoglobin. However, AE3803 seems to be the only RBC to have red hair.
  2. The bright and dark colors of the reversible jackets appear to be modeled after the colors of blood when oxygenated and deoxygenated, due to the changes in oxyhemoglobin and deoxyhemoglobin in the arteries and veins.
  3. As mentioned above, one of her nicknames is Big Sister Red Blood Cell which is a reference to how red blood cells and Platelets share the same ancestry of cells.
  • In the manga, a stem cell said “she’d probably turn out to be a dummy”- Erythroblasts and Myelocytes (Manga) and was a reference to her being an (as AE3803 says it): “A directionally challenged dummy” - The Circulatory System (Anime).
  • Like all RBCs her hat is the only (known) hat that is shaped like the actual cell shape.
  • Her birthday is on September 26.
  • The "AE" on her hat refers to her being hemoglobin E trait, a mild form of anemia caused by a genetic mutation. This explains her "airhead" personality as she's less efficient than other (AA/normal) RBCs at gas transport.[1]


  1. Rochester Medical Center[1]