Naoya Mukai is in a relationship with Saki Saki, but another girl, Nagisa Mizuse, asks him out. He makes the unthinkable decision of asking them if they would be up for both dating him at the same time.
Naoya, Saki and Nagisa are now living together. Keen to learn more about Saki and Naoya, Nagisa gets into her phone and looks through her browser history.