Akito Himenokouji and his twin sister Akiko are close - in fact, maybe a little too close for Akito’s comfort, as his sister has an unrestrained brother complex! Though her brother doesn’t take her lustful feelings seriously, Akiko is determined to set the record straight with the other ladies around him, including the three other beauties that live in his dorm and want the boy for themselves. Every morning, noon and night, the girl continues her mission to cross the line with Akito, and she won’t let any girl or sense or morality get in her way - for as long as there’s love, it doesn’t matter if he’s her brother!
Shougo Mikadono’s deceased father left his son with a final request: attend his old high school to search for a suitable spouse, get married, and take his place as the rightful president of the prestigious Mikadono Corporation. Eagerly accepting the criteria, the teenager enrolls and quickly garners the attention of class rep beauty Konoe and one wealthy maiden after another due to his illustrious family legacy. What's more, Shougo then receives a very unexpected phone call from an unknown fellow student claiming to be his long lost sister - and she, too, wants to marry him! Can Shougo restrain his youthful desires while lustful beauties throw themselves at him in school, at home and even in his own bed long enough to determine who among them is his hidden little sister?
These two anime have very similar themes- romance/comedy, harem, and incest. As the male lead tries to avoid sibling love, he ends up meeting a bunch of girls who become romantically interested in him.
Both animes are about sisters that want to get with their older brothers; which, are also both harem series. While Onii-chan Dakedo Ai Sae Areba Kankeinai yo ne! has the sister living with him, in Kono Naka ni Hitori, Imouto ga Iru!, she remains hidden among his haren.
Good-looking Kanade Amakusa would prefer nothing more than to have a normal high school life. But due to his "Absolute Choice", a mental curse compelling him to decide between two outrageous options such as sniffing a smutty magazine on the ground versus eating it in public, everyone thinks he’s a total weirdo! One day, the boy chooses that a beautiful girl will fall from the sky, and much to his surprise, his choice becomes reality! Her name is Chocolat, and she’s come with a message: God will strike a deal with Kanade in the form of missions that might just cure his suffering. Sounds trouble-free enough compared to what he’s already gone through - except they’re on a whole other level of extreme craziness than the choices he already makes daily! Can Kanade successfully clear these outrageous challenges, or will he be forever rejected by his classmates and remain an outcast?!
A guy is surrounded by women of varying... levels of sanity but all have feelings for him because not only is it apparent, but it's funny! The guy gets into uncompromising situations, perverted situations, possibly misunderstood by the school and best of all, tries to take it with a grain of salt, the straight man to the world of crazy. A near-deadpan response to the insanity-laden school girls that gravitate to his charm. Sure one's part student council of questionable notoriety and the other one is part of a near equal number of notorious "undateables" or "strange bunch of characters" but in the end, the humor is there and it's a guy just trying to get by in his harem/comedy school life show.
If you like one,then you will like the other because both animes have guys surrounded by girls and they also have several perverted situations.
Although they are not related by blood, Keita finds himself the object of his feisty twin-sisters Ako and Riko’s affections. Using extremely creative ways to wake him in the morning, the girls kiss, caress and grope their way into Kei-chan’s bed in the hope of becoming his bride. Forbidden sibling love even spreads to the school classroom, and as the rivalry between Ako and Riko intensifies, will they stop at nothing to win their brother’s unwilling heart? But how far is too far, and can Keita say no to two beautiful young girls throwing themselves at him forever?
Mitsuki and Yuuya have just become step-siblings, and are working to adjust to their new lives as a family living within the same house. While Mitsuki is cautious of this new relationship with her ‘older brother’, her inhibitions quickly take a turn for the perverted when she’s suddenly possessed by Hiyori, a ghost girl with amnesia. As if things couldn’t get any worse, Hiyori forcibly outfits her with a chastity belt that’s so restrictive it often causes the girl to pee herself - not to mention, in order for Hiyori to finally reach heaven, Mitsuki needs to experience a certain amount of sexual pleasure and energy… with her big brother! Now, between trying to not soil herself and trying to get used to Hiyori’s hands between her loins, Mitsuki will do her best to survive her new "family" life with, or without, her virginity intact.
Both follow a brother and sister who aren't related as the sister works towards her ultimate goal of banging her newly gained brother. Both are ecchi, both are distasteful, and both are also pretty bad.
The main difference is that while in Onii-chan Dakedo Ai Sae Areba Kankeinai yo ne! the sister actively wants to chase after her brother, the sister in ImoCho is forced to by some ghost rapist, who will literally kill her if she doesn't sleep with her brother.
Oh, and ImoCho loves urine fetish. So you know, if that's your kind of thing then you're in for a treat. Probably.