Psi recurs as a core character across multiple installments of the educational franchise, consistently portrayed as a child in the macroscopic human stories alongside Pierrot and others. These segments depict Psi participating in everyday activities like outdoor play, school life, and family dynamics, often transitioning into explorations of physiological processes.

Within the microscopic setting representing bodily systems, Psi transforms into an anthropomorphized B lymphocyte, defending the human body. Piloting a compact spacecraft equipped with hydrojet propulsors and an underbelly bomb bay for antibody deployment, Psi actively patrols the bloodstream and tissues. The character identifies and combats pathogens such as bacteria and viruses using targeted antibodies, coordinating immune responses with other defense cells including T lymphocytes and phagocytes.

Psi's adventures extend into the space exploration-themed installment, appearing as a companion to Pierrot during interstellar missions. These journeys involve confronting galactic conflicts and encountering diverse alien civilizations. This cross-series portrayal maintains Psi's signature design and collaborative role within the ensemble.

In both the physiological and space-faring contexts, Psi operates as part of a team, frequently collaborating closely with characters like Peter (another lymphocyte pilot) and Lieutenant Claire during immune defenses. Psi's design remains consistent: a youthful humanoid appearance featuring stylized attire appropriate to each setting, whether as a child in framing stories or as a specialized cell within the animated bodily landscapes.