From Liquid Passion:
Tensions build during zero-unit training, and Asaoka finds himself throwing a punch in Shiki’s defense. When supervisor Takano confines him to his room, Asaoka gains a rare opportunity to talk once more with his crush, which prompts him to reassert his romantic interest. However, will the unexpected fallout from the disciplinary action added to the stress of training sabotage the progress of their relationship?
You can read it here: http://www.mangafox.com/manga/calling/
Part of a serie: