Well, surprisingly the last thing you would want to be concerned about is accidentally mistaking your unknown long lost step sister for her.
And this is where we find our story's main character Shogo, as he worries his way through school life attempting to uncover the identity of his sister, and keep himself from falling too into trouble with the girls that have suddenly come out of the wood-work to cling and fawn over him.
Kono Naka ni Hitori Imouto ga Iru is similar to a lot of the "sister" themed anime out there, and at first, it seems that it's just a rehash of sorts. But after episode one, it's clear the real key point of this story is, and the real hook to it, is the mystery surrounding the unidentifiable "Imouto".
Sure the show has plenty of boobs, and panties, and nudity, and I'd love to sugar-coat that into some sort of reasoning, but I just can't. It's a perv's paradise. But one thing this isn't... is nasty. While the girls are all but throwing themselves at Shogo, there is still this sense of self-respect and charm that comes from the poor chap, and even though he has to endure a lot of hardship with his future relationships, he isn't the stereotypical victim of the series either. in fact for a guy in a modern harem, he has it pretty good, and I think he knows it.
As the series progresses, things get more and more steamy, and for a show that seems to know where the lines are drawn, it manages to push every one of them almost to the point of breaking, but as a viewer we are just riveted to the screen, watching all the awesome with bated breath.
As of this posting, there have only been ten episodes aired in Japan, of Kono Naka ni Hitori Imouto ga Iru, and this last arc could prove to make or break our beloved main hero.
Will he find his sister? Will he find a bride? Will he prove to be successful enough to claim his father's empire?
We'll just have to wait two more weeks to see.
A must watch, for anyone that loves the harem genre, and doesn't mind some T & A.