One year has passed since the events of Ninisanni Scenario 1, and MC-kun is depressed... again. But this time it's for totally non-trivial reasons! Despite securing a harem of nine lovely ladies, he has some (cowardly) latent guilt stemming from the fact that his "harem" is just him sleeping with nine girls simultaneously without them knowing about each other.
But that's peanuts compared to the big bad news... Pomu is gone! And we don't know where she went! She didn't even send a postcard! And you know she's the type to send postcards!!
But despite all the spooky mystery and intrigue, really, most of the time is just the troublesome goofs hanging out and causing trouble. What better way to spend a summer?