Himari Akeno can't wait to start high school! Even though she's parting ways with her twin sister, Mio, Himari's enthusiasm to start this new chapter of her life is palpable—that is, until a traumatic incident sends her home to hide in her room...Watching Himari's dreams shatter is more than Mio can bear, especially when her sister still longs for an ordinary student life. Determined to see her twin get back out into the world, Mio "catches a cold" and convinces her sister to fill in until she "recovers." As long as the shy, introverted Himari can pull off impersonating the bubbly, energetic Mio, nothing could go wrong...right?