What is Nakaimo? The story is set up pretty clearly by our main character's mother, see below:

In the very first episode, we see Shougo Mikadono mourning his father's passing. It seemed that he had a close relationship with him, despite going against the grain of large, rich families and their parent-child relationships. Shougo hears a mysterious voice at the funeral, and this voice claims to be his long-lost sister.

It all seems sensible from a set-up perspective until we see Shougo attending his new school. The entire school knows him, and even if it may not be the case, everyone who is interested in Shougo is some kind of girl? Even the innocent bystander that Shougo tried to save (Konoe Tsuruma) secretly wants to get into his pants? The tree-climbing tsundere, after spoiling Konoe's attempt at snuggling up on Shougo, also expresses interest? And then there's the girl in a witch's hat? I guess going by the opening animation, not all the regular casts have been introduced yet.

As for now, the main story has to do both with why all the girls want to jump Shougo, and also the clues that leads to both his traumatic past, his potential long-lost sister, and what it all has to do with a toy robot and his scar. There's a fair amount of bait from the first episode to set all the groundwork.

Of the ongoing trends in today's anime, adaptation from light novels has to be one of the more exciting things. Unfortunately, a lot of light novels today are, well, questionable. Some of them have some pretty odd names, others have shady titles that befit butts of jokes. But those things often don't indicate quality or how well the adaptations turn out.

I'm hoping Nakaimo bucks its big-bro-little-sis title, its harem structure, and the usual trapping of moe pandering trends. At one episode, it's way too early to say; hopefully in three episodes we can make a better call. At this point, I can only pray to God and hope for the best.