People brought here by the "ads", sorry to disappoint but it's not ecchi. It's just really effing cute.
But the topic? The topic is WEIRD. The setup is just... try explaining that. And there are a couple of fairly "yikes" chapters, I'm not gonna sugarcoat it. And certain aspects of the story (i.e. Mahiro's closeness to Momiji) are things you might not want to think about too hard.
But it's surprisingly a cute story about a little sister who, with the power of science, helps an extremely dysfunctional adult brother get a second chance as her own little sister. Is he done for? We'll have to see!