“Overnight, my gender changed.”
Oh Ha-rin and Morgan, childhood friends who grew up separated by only a wall.
One day, Oh Ha-rin , who is afflicted with TS disease (a disease where gender changes randomly), appears at school as a woman.
Everyone is unfamiliar with her—except for one person, Morgan, who recognizes Oh Ha-rin 's eyes.
A youth romance mystery that begins amidst familiarity and unfamiliarity, excitement and confusion.
A secret that cannot be told to anyone.
A special story shared only by the two of them.

Oh Ha-rin
• Default Gender: Male (Possesses TS disease)
• Height: 178cm when male / 163cm when female
• Personality: Outwardly quiet and indifferent. However, internally, there is constant confusion and resistance about his own existence. The only time he can laugh comfortably is in front of Morgan.
• Conflict: His life is completely turned upside down due to the sudden onset of TS disease. In the midst of clashes with everything he was familiar with, his relationship with Morgan in particular begins to waver.
• Characteristics: Doesn't trust people easily, but Morgan is an exception.

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Morgan
• Gender: Undetermined (Not specified)
• Appearance: Round eyes and a bright smile are her trademarks. She maintains a neat style, but always exudes a somewhat disheveled atmosphere.
• Personality: Cheerful and optimistic. Generally positive and easily gets along with people. However, she has a hidden sensitivity that remarkably notices changes in people very close to her.
• Relationship: Oh Ha-rin and her have been neighbors since childhood, separated by only a wall. She often jokingly said that she would always be on Oh Ha-rin 's side no matter what, but she never thought that those words would be put to the test.
• Characteristics: Seems thoughtless on the surface, but has a stronger belief than anyone else in what she loves. She instinctively reacts to Oh Ha-rin 's changes and is ready to stay by his side until the end.