My beloved "Little Princess" girlfriend was already trained

The protagonist, Ritsu, has a girlfriend named Sarina who is from the same class.
Sarina keeps her distance from her lively classmates and
has a quiet personality, reading books in the corner of the classroom.
Due to her small stature and neat appearance, her classmates nickname her Princess.
Sarina and the kind-hearted and slightly shy Ritsu are on the same wavelength, so they slowly
get along at their own pace and deepen their bond. Ritsu dreams of one day being able to have a deeper, more loving relationship, but he doesn't know that Sarina's body has already been completely violated by her uncle...