Nanakakusui no Shoujo Reveals Cover Ahead of October 22 Release

SB Bunko has unveiled the cover for Nanakakusui no Shoujo (七角錐の少女), a new novel by Yomoji Otono (乙野四方字) with cover illustration by Shion (しおん). The book is scheduled to release in Japan on October 22, 2026.

Its currently revealed premise is deliberately concise: a heptagonal-pyramid-shaped mansion stands in a remote mountain village surrounded by bamboo, where seven boys begin disappearing one by one. SB Creative leaves readers with one additional clue—their fate lies within a regular heptagon.

Quick Summary

• Title: Nanakakusui no Shoujo
• Japanese title: 七角錐の少女
• Japanese reading: ななかくすいのしょうじょ
• Format: novel / entertainment literature
• Publisher category: general books / SB Bunko
• Author: Yomoji Otono
• Japanese author name: 乙野四方字
• Illustrator: Shion
• Japanese illustrator name: しおん
• Publisher: SB Creative
• Imprint: SB Bunko
• Status: available for preorder / unreleased
• Cover reveal: September 2026
• Japanese release date: October 22, 2026
• Price: ¥880 including tax
• Base price: ¥800 before tax
• Physical format: bunko
• Page count: 320 pages
• ISBN-13: 978-4-8156-4717-9
• ISBN-10 / Amazon ASIN: 4815647178
• Premise location: remote mountain village surrounded by bamboo
• Central building: a heptagonal-pyramid-shaped mansion
• Number of boys in the premise: seven
• Core incident: they disappear one by one
• Official clue: their fate lies within a regular heptagon
• Specific official genre: not yet detailed for this title
• Premise tone: mystery and suspense
• Identity of the cover girl: not detailed in the verified public information
• SB Bunko position: one of its debut titles
• October launch lineup: eight books
• SB Bunko launch date: October 22, 2026
• Imprint positioning: a new entertainment literature label from SB Creative
• Publishing schedule: every fourth Thursday of the month
• Label range: youth, romance, mystery, suspense, horror, workplace fiction and other entertainment fiction
• Anime / film / manga adaptation: unannounced
• English edition: unannounced

Cover and Novel Announcement

Shion's Cover Brings the Mountain Village Into View

The newly revealed cover features a long-haired girl in a white dress against a broad rural and mountainous landscape. Bamboo visible along the composition also matches the official description of a remote village surrounded by bamboo groves.

The girl's identity, her connection to the seven boys and her place within the story have not yet been explained by SB Creative. The artwork alone therefore does not establish whether she is the protagonist, a resident of the mansion or someone occupying a different role in the mystery.

The cover illustration is credited to Shion, as confirmed in SB Bunko's official announcement.

Seven Boys Disappear From a Heptagonal-Pyramid Mansion

The official premise places the story in an isolated mountain village. Rising within it is a structure described as the Nanakakusui no Yakata, a mansion shaped like a heptagonal pyramid.

Seven boys stand at the center of the situation, only to begin disappearing one after another. Nothing currently confirms whether those disappearances involve a crime, a supernatural phenomenon, the mansion's architecture or some other mechanism.

The recurring promotional line says that their fate lies within a regular heptagon. The relationship between the number seven, the building's geometry and the missing boys appears to be a central puzzle deliberately being kept unresolved ahead of publication.

320 Pages for ¥880 on October 22

SB Creative will publish Nanakakusui no Shoujo through SB Bunko on October 22, 2026.

The standard edition costs ¥880 including tax, uses a bunko format and contains 320 pages. Its official ISBN-13 is 978-4-8156-4717-9, while Amazon Japan uses 4815647178 as the ISBN-10 and product identifier in its listing URL.

Preorders are already open through Japanese retailers including Amazon Japan and Rakuten Books.

One of SB Bunko's Eight Launch Books

Nanakakusui no Shoujo's publication date is also the official launch day of the new SB Bunko imprint.

SB Creative describes SB Bunko as an entertainment literature label, and the publisher categorizes this title under General Books → SB Bunko rather than its GA Bunko light-novel category.

Eight books are scheduled for the first wave on October 22. SB Bunko plans to publish new titles every fourth Thursday, covering youth stories, romance, mystery, suspense, horror, workplace fiction and other forms of entertainment literature.

Yomoji Otono Returns to a High-Concept Setup

Yomoji Otono began his novel career in 2012 after receiving a Selection Committee Encouragement Award at the 18th Dengeki Novel Prize, leading to the publication of Minutes: 1-punkan no Zettai Jikan.

He later became widely known for the paired novels Boku ga Aishita Subete no Kimi e and Kimi wo Aishita Hitori no Boku e, which were released simultaneously and eventually developed into anime films.

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Kodansha's official author profile highlights Otono's strength in tricky, high-concept ideas. Nanakakusui no Shoujo immediately presents another unusual framework by making seven characters, a regular heptagon and the geometry of a mansion central elements of its setup.

Why This Matters

1) Geometry is built directly into the mystery

The title, central building, number of boys and official regular-heptagon clue all revolve around the number seven.

2) The premise is compact but leaves major gaps intentionally

SB Creative has revealed the location, seven boys, their sequential disappearances and a geometric clue without explaining the underlying cause.

3) It arrives on SB Bunko's first day

The novel is not only a new Yomoji Otono release but one of eight books opening SB Creative's new entertainment literature imprint.

4) The cover does not immediately explain the premise

Shion's artwork prominently features a girl whose identity remains unexplained, while the public synopsis currently centers on seven boys.

Novel Information

For now, the additional important information currently known includes:

• Nanakakusui no Shoujo is a novel by Yomoji Otono
• its original Japanese title is 七角錐の少女
• the Japanese reading is ななかくすいのしょうじょ
• Shion is responsible for the cover illustration
• the novel is published by SB Creative
• its imprint is SB Bunko
• SB Creative classifies it under general books / SB Bunko rather than GA Bunko light novels
• the Japanese release date is October 22, 2026
• the regular edition costs ¥880 including tax
• the pre-tax price is ¥800
• the physical edition uses a bunko format
• the official page count is 320 pages
• the ISBN-13 is 978-4-8156-4717-9
• the ISBN-10 is 4815647178
• Amazon Japan uses 4815647178 in the product URL
• preorders are already open ahead of release
• the premise takes place in a remote mountain village
• the village is described as being surrounded by bamboo
• a heptagonal-pyramid-shaped mansion stands there
• seven boys form the center of the premise
• the boys begin disappearing one at a time
• the official clue says their fate lies within a regular heptagon
• the cause of the disappearances remains unannounced
• the identity and role of the girl on the cover remain unexplained
• main character names have not been announced in the verified public material
• the book's specific official genre is not listed on its product page
• no anime, manga, film or drama adaptation has been announced
• no English or global edition has been announced
• the book is one of eight titles launching SB Bunko
• SB Bunko officially begins publishing on October 22, 2026
• SB Bunko is positioned as an entertainment literature label
• regular SB Bunko releases are planned for every fourth Thursday
• the imprint covers youth, romance, mystery, suspense, horror, workplace fiction and other entertainment storytelling
• Yomoji Otono debuted as a novelist in 2012
• his earlier works include Boku ga Aishita Subete no Kimi e and Kimi wo Aishita Hitori no Boku e
• Kodansha's profile describes Otono as a writer known for unusual high-concept ideas
• official book information is available through the SB Creative Official Book Page
• imprint information is available through the SB Bunko Official Website
• current updates are published through SB Bunko Official X
• the cover reveal is available through the Official X Post
• the debut lineup is available through the SB Bunko October 2026 Lineup
• author information is available through the Kodansha Taiga Yomoji Otono Profile
• Japanese preorders are available through Amazon Japan
• an additional product listing is available through Rakuten Books

Closing

Nanakakusui no Shoujo begins its promotional campaign with a sharply defined setup: seven boys, a heptagonal-pyramid mansion and a sequence of disappearances tied to the image of a regular heptagon. Shion's newly revealed cover now gives the novel a clearer visual identity ahead of publication.

The book releases in Japan on October 22, 2026 as part of SB Bunko's debut lineup. Character identities, the mechanism behind the disappearances, the true structure of its mystery and any potential media adaptations remain unannounced.