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Cho Chang is introduced during the Third book as the Seeker for Ravenclaw's Quidditch team. Harry describes her as being pretty, though he makes no move to pursue her during the novel.
In the fourth book, Harry has a crush on Cho. He wants to ask Cho to the Yule Ball, but once he finally gets his courage up to ask her, she is already going with Cedric Diggory. Cho dances with Cedric a lot at the ball, and Harry watches them the whole time.
In the Order of the Phoenix, Harry shows romantic feelings for Cho, and shares his first kiss with her after a Dumbledore's Army meeting before the Christmas break. As Cho was crying, Harry described the kiss to Ron and Hermione as "wet.". The trio begins to have a discussion about how CHo felt and if Harry was a good kisser or not.
She shows up for the final battle at Hogwarts. She is going to bring Harry to look at the model of the diadem of Ravenclaw, but Ginny makes Luna bring Harry instead.
Portrayals within films
If applicable, maybe 1-5 paragraphs here.
Maybe a paragraph here.
Depending on how often the character is in the books, maybe 1-5 paragraphs here.
Magical accomplishments and skills
If magical, maybe a 1-3 paragraphs here.
Maybe 1-3 paragraphs here.