Boy Meets Girl: Make Me Your "First"!!

We are introduced to Yamada, considered to be her high school's idol, and to her mission in life in high school: to obtain a hundred sexual partners. However, she is rather picky, and decides to concentrate on a guy named Takashi Kosuda, whom she meets at a bookstore while shopping for a dictionary; and her would-be classmate. She then steps her campaign up a notch by finding a way to go home with Kosuda so that she can "get him." She is able to even get into his room; and seemingly with his liberated sister Kazuki's "blessing." However, her inexperience scares her to death that she rushes out of Kosuda's house in haste.