You wake up with a pounding headache in a room that looks like your own, but doesn't feel quite right. By your bedside is a cute girl who introduces herself as Nagi, your adorable, doting girlfriend. Nagi informs you that you're very sick, but don't worry: she's going to do her very best to take care of you! That would be all well and good, but... If Nagi really is your girlfriend, why can't you remember her?