The Evil Young Man's Contract Wife

Wu Han, Yi Ran was married by his parents when he was not born. Yi Ran did not know his parents' agreement and took care of Wu Han and thought it was his brother's affection for his sister. However, Wu Han knew since he was a child that this cute little sister would be his wife in the future. In order to prevent others from having designs on Yi Ran, he took the initiative to stay in grade to be with her until Chen Chen appeared. How would they change?