I'm a librarian who loves anime, manga, and reading a wide variety of genres.
I'll start by saying that the description on the back of the volume contains several incorrect statements. There is no evidence that Souji's sisters' clingy behavior is anything new. Also, I don't know if Souji and Yukako start dating in the next volume, but Yukako is not Souji's new girlfriend in this one. Now, on to my description.
Souji is a high school student who left his family home some time ago. He had hoped never to return, but sometimes we don't get what we want. At any rate, his three sisters are thrilled he's back. Harumi, his stepsister, is sweet and quiet and clearly has a crush on him. The real problems, though, are Youko and Saki. Youko is Souji's full sister. She possibly has a split personality, and she's certainly a vaguely malevolent presence in the household, glaring daggers at Souji even as she cuddles up to him in a more than sisterly sort of way. Saki is the daughter of Souji's father and Souji's father's mistress. She works as one of the family's maids and, when the other sisters aren't around, sleeps with Souji. And possibly also Kazushi, Souji's older brother. Kazushi, meanwhile, may be lurking somewhere nearby.
At school, Souji instantly comes to the attention of Yukako, the self-proclaimed sole member of the student council's “Intelligence Committee.” It's Yukako who tells Souji of the three murders that occurred at the end of the summer, shortly before he arrived. The school's smartest student was stabbed. After that came the track team's star runner, also stabbed. Then the student council president was pushed in front of a train. Yukako wants to know why the killer chose those particular victims, especially since she had a crush on the student council president. She basically forces Souji to join her, but Souji secretly thinks he knows who was responsible: Youko, his sister.
I think I picked this volume up in the clearance section during a used book shopping trip. I wasn't aware, at the time, that this was only a 2-volume series. It wouldn't be hard for me to either buy the second volume or get it via interlibrary loan, but...I don't know that I want to. Even that small amount of effort feels like too much.
This series' vibe reminds me of When They Cry, only with added incest and less playing around with tropes. Souji is a boring blank slate. He's supposedly good at everything – a star athlete, top student, handsome enough that all the girls fall for him (including all of his sisters) – but if Yukako hadn't repeatedly said how awesome he was, I'd have guessed he was a stereotypical loner geek with no friends and creepily affectionate sisters.
The creepy sisters thing was apparent right from the start, although the only one who seemed to genuinely creep Souji out was Youko. He took Harumi's devotion in a stride and saw it as destiny that he and Saki regularly slept together. I had a feeling he would have easily accepted Youko's habit of draping herself on him all the time if she hadn't also radiated hostility. The first time readers saw her, she was standing at the other end of a dark room, glaring at Souji. Also, when she unexpectedly visited Souji's school, Souji could sense her presence well before he saw her, in the form of a chill running down his spine.
This first volume was jam-packed with mysterious elements: Souji's gross relationship with his sisters, the murders, the hints that Souji's older brother was lurking somewhere in the background but refusing to reveal himself, Souji's reason for leaving in the first place, the possible references to “other selves” (either other personalities or doppelgangers), and the hints that Souji and/or Youko and Saki had previously killed someone.
I'm just not sure I have it in me to care. Souji was a boring guy who only got involved in the murder investigation because Yukako dragged him into it, and his relationship with his sisters was extremely off-putting. The storytelling was sloppy and unfocused, especially for something that was going to wrap up in only one more volume. And I shouldn't have to find out the answers to certain questions, like “why does Saki work as a maid in the family's household?”, by reading the character profiles.
(Original review, including read-alikes and watch-alikes, posted on A Library Girl's Familiar Diversions.)