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From Strawberry Vanilla:

One day a girl named Koyori Fujimoto is pulled out of a crowd while watching a magic act on the street and is forced to participate by getting into the 'Miracle box' and being made to 'disappear'. What really happens is she suddenly finds herself being carried over the shoulder by someone, down a ladder into the sewer below the street. Turns out the guy is part of the magical act. When Koyori gets a good look at him, she is stunned at how good looking he is, and by his one brilliant emerald eye, and other brown eye. Koyori is fascinated by him and asks his name, and he tells her it's 'Yuki' and then he rides off on his motorcycle. At school the next day, Koyori is preoccupied by thoughts of Yuki, but she also catches a few glimpses of an old crush, Shuu-kun. We see that Koyori's class is taught by a very geeky looking guy with glasses named Nagase-sensei, but turns out he is Yuki!! Now Koyori is caught in the middle between her feelings for her classmate Shuu-kun, and her new feelings towards her surprisingly handsome teacher.