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Oh Seung-Pyo has always been at the top of his class, but once he enters high school, his spot gets stolen by Ryu Jae-Min. No matter how hard Seung-Pyo tries, he can't seem to reclaim his place and is stuck in second. For the first time in his life, he develops an inferiority complex and, without realizing it, he starts keeping an eye on Jae-Min. One rainy day, the two accidentally swap phones. Though it seemed like a minor accident, what Seung-Pyo discovers on Jae-Min's phone leaves him in shock, complicating their relationship beyond expectation.