Yesterday Taguchi is a university student with a dissolute nature, bearing the full Japanese name 田口イエスタディ (Taguchi Iesutadi). He aspires to become a manga artist, driven by a sense of artistic calling, yet frequently struggles with deadlines and faces professional conflicts due to procrastination.

His personality includes voyeuristic tendencies; he often rationalizes inappropriate behavior using pseudophilosophical explanations about eroticism and human psychology, falsely claiming physical boundaries are irrelevant because all body parts interconnect through the skin. Taguchi exhibits significant anxiety about his codependent relationship with fellow student Makiko Gregory, often breaking into cold sweats while attempting to conceal his infidelity with classmate Miwako Mizukoshi. Despite frequently complaining about the dysfunctional dynamic with Makiko, he perpetuates situations ensuring their codependency continues.

Physically, Taguchi has black hair and a receding hairline, a sensitive subject for him. Stress triggers visible hair loss, and he reacts strongly to threats against his hair, such as Nanako Matsutaka's warnings to pull his bangs if he oversteps boundaries. His appearance and mannerisms contribute to his role as a perpetually anxious and conflicted individual within the academic setting.