High school teacher Sei Sakura is feared by her students as a rigid hard-ass who doesn't tolerate even the slightest rule violation. However, her so-called 'Iron Mask' persona is actually just a front to hide her naturally timid personality; she’s simply acting the part of a 'proper teacher' to appear like a decent adult. The one person Sakura struggles with most is Belle Makimura, a free-spirited transfer student who couldn't care less no matter how many times she's reprimanded. While Sakura considers Makimura her natural enemy, their relationship begins to shift after she accidentally discovers a certain secret...