Zenbu Kimi no Sei da.

"Sutora Iga is a student at a certain girl's school in Tokyo. She's on the more petite side of her class. Despite looking like just a normal student, she would act unbefitting of her age at times. A taciturn girl who doesn't have many friends. But, I saw her hiding her face while outside of school. Maybe she secretly meeting someone? She has good grades for every subject except P.E. However, I'm worried about her future as she wrote "mooching off old men" in her Career Planning Survey. I honestly don't know whether she was just joking or being serious. She has a very lascivious look in her eyes. Sometimes, she would look at me like a carnivore staring at its prey. I need to do all I can to not be alone with her. She's Someone who I have to stay on her good side after she graduates." (According to her homeroom teacher's notes.)

[Source: End of First Chapter]