AC1677 was a red blood cell who worked within a poorly maintained body characterized by an abusive work environment. He formed a close friendship with another red blood cell, AA2153, during their younger years together at bone marrow school.

In physical appearance, AC1677 stood slightly shorter than his friend AA2153, though his anime depiction showed him as taller. He had straight blonde hair that reached his chin and was most often depicted with his eyes closed.

AC1677 possessed an easygoing nature and frequently slacked off from his duties by resting at the capillaries. Chicken-hearted by nature, he often attempted to escape whenever hardships occurred, believing he would be unnecessarily putting himself in danger. Despite this tendency, he typically continued with his work because of AA2153's strong commitment to duties.

After AA2153 received Top Rookie honors, AC1677 experienced feelings of inferiority and began distancing himself from his friend. He vented his frustrations and believed it best not to associate with a "role model" like AA2153. This distancing led him to associate more with irresponsible veteran red blood cells who introduced him to caffeine and arginine, resulting in AC1677 developing an addiction.

This addiction nearly cost him his life during a nosebleed incident. He recovered through AA2153's encouragement and his friend's admission that he valued their friendship. The experience reforged their bond and made AC1677 more responsible in his approach to work.

AC1677 ultimately demonstrated his loyalty by sacrificing himself to save AA2153 from falling into stomach acid.