Is insanity hereditary? Shougo Mikadono’s beginning to think so, because the terms of his late father’s will seem crazy and following them may drive Shougo bonkers as well. Oh, it sounds simple at first: before Shougo can claim his VERY large inheritance, he just has to start attending a certain new school and find a nice girl to marry. Unfortunately in Shougo’s case, that Ms. Right may end up being a little TOO familiar…as in, familial! Can he find his future bride without slipping into the wrong set of genes? Find out as family planning takes on a whole new meaning in NAKAIMO - My Little Sister is Among Them!
During his father's funeral, Shogo is startled by a voice outside his window. The voice claims to that she is his little sister, but before he can learn who it is, he finds out the conditions of his inheritance.
Shogo receives a mysterious call from a person who claims to be his sister. Meanwhile, his school life gets a jolt with the arrival of a new student to his class.
Shogo's sexual preferences come into question, causing Miyabi and Rinka to overextend in their efforts to show him the appeal of a woman.
Shogo's relationship with Myabi lies in ruin. A new problem arises after he tells Konoe about his dilemma.
Shogo discovers someone else has the same prototype phone as Konoe.
Shogo concocts a plan to prevent Lyrical Sisters from shutting down.
Shogo's "sister" demands that he stop looking for her or else she'll reveal damaging secrets via the school broadcast system!
Kunitachi might be the Shogo’s sister but he can’t get close to her. Ikusu suggests that Shogo and Kunitachi spend time outside the school to have her drop her guard.
Shogo is getting a new neighbor and an unexpected surprise!
Things get messy when all of Shogo's potential wives are invited to the same party. Just when he thinks things can't get any worse, he learns that a trusted family member is plotting to overthrow his inheritance.
Kannagi’s outrageous demands in addition to all the chaos and adversity he is already facing is causing Shogo to lose his mind!
With Ikusu’s help, Shogo finally discovers the identity of his real sister.