Hayaku Shinaito Kaerenai

Childhood friends Michiru and Taichi are on their way home from high school when they're suddenly engulfed in light. The next thing they know, they're trapped in a locked room! To make things even weirder, a mysterious message tells them, "If you want to get out, kiss each other on the neck!" Seriously, what’s that about? Embarrassed but determined, the two start tackling each mission to find a way out. In this forced lovey-dovey situation, will their more-than-friends-but-not-quite-lovers relationship take a step forward? (Source: Kodansha, translated)