Living Together with Your Cute Niece

Our lonely protagonist is living all by himself in a house of his own. But everything changes for him one night when his sister calls asking if he'll look after her daughter for a while while she's away on a business trip abroad. Well, rather than ask, it's more she forced it on him, and he had no chance to refuse. He hasn't seen his niece for ages. He can only wonder what she's like now...