Neck.

Tomokazu Shudo has his first ever crush on Sugina Mayama, a senior student. Tomokazu has troubles confessing his feelings to the popular student, but one day, he is invited to the research lab where Sugina Mayama works. Tomokazu hopes to use this meeting to express his true feelings for her. To Tomokazu's surprise, when he arrives he first sees a big wooden box in the middle of the dark lab. Sugina tells Tomokazu that he looks scared and then proceeds to push Tomokazu into the box!