Tanaka-kun's Valentine

Today is Valentine’s Day. While girls and boys are excited, Tanaka, who’s not interested in Valentine’s at all, finds a box of chocolates inside his bag. Judging by the pretty box, it’s obvious the giver has feelings for him, but Tanaka feels despair just thinking about having to show gratitude or giving something in return. There’s no name on the attached message and only says “I’m watching you all the time.” Tanaka and Ohta try to figure out the culprit... i.e. the girl behind the chocolates.