Direttrice Sakurai, whose full name is Ryoko Sakurai, is the formidable chairwoman of the board of directors for the academy where the story takes place. On the surface, she presents a dual image that is central to her character. To the casual observer, she often appears as a cheerful and unassuming elderly woman who enjoys working as a vendor at the school's canteen, an activity she claims is a personal hobby that allows her to observe people in their natural state. However, this demeanor masks her true position as the all-powerful executive who holds ultimate authority over the school, capable of making significant decisions that go against the wishes of other faculty members. Her background is rooted in education, as she was once a homeroom teacher, and over the years she has cultivated powerful connections in the political and business worlds through her former students.

In terms of personality, Sakurai is defined by her sharp insight and a deep, genuine care for the well-being of her students. Despite her cold-hearted and pragmatic gaze when assessing situations, she possesses upright values and is deeply affectionate towards those under her charge. She is a patient and calculating strategist, rarely displaying emotion openly, but when provoked, especially regarding family matters, she can show a more fiery and even physical side. Her primary motivation is to reform the flawed Japanese education system, which she believes has negative effects on its youth. She sees the protagonist as the unconventional key to achieving this goal, willing to hire and protect him because she recognizes his potential to reach students in ways traditional teachers cannot.

Sakurai’s role in the story is that of the protagonist's most powerful and steadfast ally, as well as his protector from behind the scenes. She is the one who personally hires him, seeing past his delinquent history and third-rate university diploma. She consistently shields him from attempts by other staff members, such as the assistant principal, to have him fired, trusting in his unique teaching methods. Her role extends beyond a benefactor; she serves as a source of advice and a pillar of support for both the protagonist and his colleague. She is also a major authority figure whose word is final, representing a more progressive and understanding faction within the school's administration.

Her key relationships are deeply intertwined with the plot. Her most important relationship is with the protagonist, whom she respects enough to address as "sensei," trusting him even with the well-being of her own troubled grandson, Mayu Wakui. This relationship is tested when he uses force on her grandson, leading to her rare and shocking decision to slap him, which highlights the complex personal stakes involved for her. Sakurai also has a significant and complex history with Misuzu Daimon, a former student who later becomes principal. Their past involves a painful misunderstanding where Daimon felt abandoned by her during a moment of crisis as a student, leading to long-lasting resentment that must eventually be resolved.

Throughout the story, Sakurai experiences subtle but significant development. Her unwavering faith in the protagonist never wavers, but she is forced to confront her own past failures and emotional attachments, particularly through her relationship with her grandson and her former pupil, Daimon. These challenges reveal her vulnerability and the personal cost of her professional position, but she ultimately remains a figure of integrity and wisdom who reconciles with her past. Her notable abilities include her exceptional skill in reading people, which she hones by working anonymously in the school canteen. Furthermore, she wields immense institutional power, possessing the singular authority to make or break a teacher's career at the academy, as well as a vast network of influential contacts that she can leverage to achieve her goals.