|SPECIES||Red Blood Cell|
|ANIME DEBUT||Episode 1|
|MANGA DEBUT||Chapter 1|
AA2153 is one of the two protagonists of Cells at Work! BLACK. He is a rookie erythrocyte that had started working inside a poorly maintained body, and thus an abusive work environment.
This Red Blood Cell is a male with glasses and yellow pupils. He has average-length brunette hair with a strand that slightly resembles AE3803’s iconic ahoge. He wears a uniform that only differs from AE3803’s by the collar.
As a rookie, AA2153 was initially excited for his task of going to the lungs, only to find LDL's, Carbon Monoxide, and Pneumococcus along the way. He is dedicated to doing his part in helping the body, however is strongly disheartened by the awful work conditions and failure of the body to improve. He develops a friendship with a neutrophil, U-1196, who frequently rescues him and serves as a source of encouragement, as well as AC1677 a fellow Red Blood Cell with whom he frequently works side by side.
AA2153 becomes increasingly more resolute and dedicated to his job after witnessing the sacrifice and effort done by other cells in order to maintain the body, all of which undergo their respective hardships, valuing their self-sacrifice and becoming an effective and reliable worker (in the anime, he was even awarded as the top rookie for his work in increasingly dire circumstances).
He eventually suffers an emotional breakdown when AC1677 fell to his demise during the stomach ulcer incident, falling into despair and depression and skipping work due to the profound shock, and downright blaming himself for his friend's death. When a gout attacks afterwards, he finally snaps and tries to actively harm the body himself as a means of sending a message to the body's owner while unloading all the pent up frustration and stress caused by the host's malpractices that have caused the "BLACK" situation that have made every cell to live in perpetual misery. Through U-1196's help, he is able to stop blaming himself for AC1677's death while breaking in tears, eventually rejoining his work, where he is received by open arms by his fellow Red Blood Cells who no longer deem him a mere rookie. When the body survives a heart attack and begins to improve, AA2153's attitude becomes more optimistic and resolute.
After being transfused into a new body with even worse conditions, AA2153 is scorned and mocked by several local erythrocytes for his belief that this body can turn itself around. Despite this harsh welcome, he goes out of his way to encourage the other erythrocytes and cells to work harder for the body's sake, even as successive tragedies take away new friends and shake his outlook. During his separation from U-1196 in the immediate aftermath of the transfusion, AA2153 finds himself repeatedly saved by another neutrophil, J-1178, who he calls "White Blood Cell-chan", much to her embarrassment. Eventually, the deteriorating conditions in the second body strain even AA2153's hopes, but he continues forging ahead and eventually becomes a leader among the erythrocytes.
It is noted that both of as a sense of responsability and his own desperation to improve the body conditions (mostly for the sake of other cells), he has tried to overload himself with work and make it his duty to work harder and harder, upon where he has to be reminded that the body's condition doesn't depend entirely on him but is a joint effort of every cell.
- His code is written inside the back of his hat, so it is not normally visible.