Shinako Sugimoto, the eldest Sugimoto sister, is known for her playful teasing, especially directed at her younger sibling Yasuko. A former student of Fujigaya Girls’ Academy, she shares a rapport with science teacher Hinako Yamashina—a former classmate—blending casual ease with sharp insight. Though outwardly nonchalant in social settings, Shinako reveals a keen understanding of human behavior through perceptive remarks and wry wisdom.

Her lighthearted humor and witty exchanges mask a mature grasp of interpersonal dynamics, offering stability against Yasuko’s emotional volatility. Charismatic and enigmatic, Shinako’s romantic history with men and women alike has cemented her reputation as a Casanova, contrasting her otherwise detached demeanor.

Raised in a family deeply connected to Fujigaya—where her sisters Kazusa and Kuri also studied—Shinako navigates sibling relationships as both mediator and confidante. She subtly guides her sisters with quiet affection, balancing emotional distance with unwavering loyalty. Her bond with Yasuko thrives on spirited rivalry and unspoken devotion, anchoring their familial ties in humor and mutual understanding.