Ichirō Irabu holds the position of vice chairman at Irabu General Hospital, working as a psychiatrist. He presents as pale-skinned and overweight, frequently exhibiting childlike and eccentric behavior. His medical career began in pediatrics after medical school, but conflicts with child patients and a reputation for tantrums led to a transition into psychiatry. Doubts surround his actual academic performance during training, where he was considered a nuisance and frequently misunderstood lectures. Despite these quirks, he demonstrates perceptive insights into human psychology.

Irabu employs unconventional psychiatric methods. He mandates that all new patients receive a "vitamin shot" from his nurse, Mayumi, openly admitting the injection lacks medicinal properties. This ritual stems from his personal fascination with needles and observing injections. He shows fleeting interest in patients' triggers or disorders, often inserting himself into their lives outside the clinical setting, bypassing conventional therapeutic techniques. His approach typically guides patients toward self-realization rather than direct intervention, though he occasionally pursues personal gains unrelated to treatment objectives.

The character manifests through three distinct physical representations reflecting different personality aspects: an adult form with feminine traits during playful yet reasonably professional interactions; a child form when displaying unexpected maturity or focused professionalism; and a bear-masked form during interactions with strangers or acquaintances, functioning as a social facade. These forms coexist simultaneously, representing integrated facets of his character rather than separate identities, a multiplicity also reflected in shifting vocal characteristics across the forms.

Irabu maintains emotional detachment despite engaging with patients' profound psychological struggles. Superficial emotions like excitement or disappointment appear transiently, while deeper feelings such as genuine happiness or sorrow remain concealed. He demonstrates professional concern for patient well-being but avoids forming meaningful personal relationships, maintaining boundaries even with former medical school acquaintances who become patients. His motivations for psychiatry appear rooted in intellectual curiosity about human behavior rather than empathetic connection.

His personal history remains largely undisclosed, with minimal information about family beyond his father's ownership of the hospital. Socially isolated during medical training, he lacked meaningful friendships and reportedly underwent little personal change since youth. Outside professional contexts, he displays limited initiative in skill development or defensive capabilities, coupled with a tendency toward disinterest in prolonged commitments.