The character known as Keyop in the English adaptation is the youngest member of the team, originally named Jinpei in the Japanese version. He serves as the group's reconnaissance expert, a role that suits his small size and agility. His background is marked by mystery and a strong sense of familial loyalty. He never knew his parents and was found as an infant in the mountains by his teammate Jun, who raised him in the orphanage where she lived. This led to them being adopted as siblings, and Jun insisted they not be separated when they were recruited for training. Despite his youth, Keyop claims to be the last descendant of the Iga ninja clan, a heritage he takes pride in, referring to himself with a grand title.

Keyop's personality is a mix of childlike energy and surprising responsibility. He is generally cheerful, excitable, and mischievous, behaving much like a typical boy his age. However, he is also very dependable, helping his sister Jun run her snack bar and supporting his teammates to the best of his abilities during missions. His primary motivation stems from his loyalty to his adopted family and his team. He deeply respects the team leader, Ken, whom he calls aniki, a Japanese term for an older brother figure, and he heeds his orders without question. He also enjoys playfully teasing Jun about her feelings for Ken, showing a normal, sibling-like dynamic.

In the story's original Japanese context, Keyop is a bright and insightful child who speaks clearly. However, the English adaptation significantly altered his characterization. In this version, Keyop was reimagined as an artificial life form, a genetically engineered clone, which resulted in a severe speech impediment. Consequently, he speaks in a distinctive manner, often stuttering and making clicking, chirping, and whirring noises instead of forming complete sentences. This change was made by producers who wanted a funny-sounding child character, contradicting a long-standing fan rumor that the speech impediment was created to censor profanity from the original Japanese dialogue.

Keyop's most notable abilities are tied to his role as the team's scout. His small stature allows him to access areas the others cannot, and his training makes him incredibly agile. As a member of the Science Ninja Team, he is highly skilled in a unique and violent form of martial arts known as Science Ninja Arts, or Kagaku Ninpo, which allows him to perform superhuman feats. He wears a bird-themed battlesuit styled after a swallow and uses a special wrist device for communication, tracking, and transforming into his battle gear with the command "Bird, Go!". Over the course of the story, Keyop's development is shown through his growing competence in the field, gradually proving that his youth is not a liability but an essential asset to the team's success.