This one has been confusing people in the west since it was first announced. Based on a popular light novel, Ore no Imouto ga Konnani Kawaii Wake ga Nai, this is the second game based on the IP which has also spawned a radio series, an anime and a manga. So it's no wonder that My Little Sister Can't Possibly Be This Cute Portable: Can't Possibly Continue is top of the Japanese charts this week.
The story isn't quite what it sounds like from the title, but it's close. After not getting along with his sister for quite some time, Kyosuke discovers a DVD and, inside the case, an erotic game. He confronts his sister and discovers she's a secret Otaku and soon becomes her confidant, dealing with the outcome of his sister's collection.
The chances of this ever coming over here is fairly low and you only have to look at comment sections everywhere since this news broke to find out why. Still, if newspapers are constantly up in arms over blood and violence, I'm not sure what they'd make of this.