Chitose Is in the Ramune Bottle, Vol. 5 (manga)

Yuzuki Nanase thinks she's being stalked, but she has no proof. After opening up to Saku Chitose about her fears, she begs him to pose as her pretend boyfriend to help keep her safe. But Saku has a condition, and it turns out to be something more vigorous than Yuzuki expected...!?