Mori Basil's 'Detective Koishi Doesn't Fall in Love' Surpasses 100,000 Copies! Sequel 'Detective Koishi Will Not Return' to Release September 30, 2026!

Mori Basil's sensational mystery novel 'Detective Koishi Doesn't Fall in Love' (released September 18, 2025, by Shogakukan) has officially surpassed 100,000 copies in sales, drawing widespread acclaim for its unprecedented reading experience!

Moreover, the long-awaited sequel, 'Detective Koishi Will Not Return,' has been confirmed for release on September 30, 2026! The story continues with the detective's essential weapon—'reversal thinking'—promising a series of shocking twists that will once again thrill readers. The sequel will also be serialized in two parts on the literary website 'STORY BOX' over two consecutive months, with the first part scheduled for July 10. Experience the opening of this new chapter ahead of the official release!

First Installment: 'Detective Koishi Doesn't Fall in Love'

A full-fledged mystery from multi-talented author Mori Basil, offering a stunning reading experience. Koishi, a mystery-obsessed detective who dreams of elegantly solving difficult cases, becomes entangled in a major incident while handling love-related investigations—readers await a series of shocking developments that defy all expectations.

Immediately after its release in September last year, social media exploded with praise: 'I was completely stunned by the truth,' 'This is a book I need to discuss with others who've read it,' 'The banter between the detective and his assistant is perfect!' The novel rapidly topped bestseller charts nationwide. Nominated for the 2026 Bookseller Award, it also won first place in the MRC Award 2025, the Miyabon 2025 Award, and the 14th Yuuharu Prize, ranking highly in multiple annual mystery rankings—making it the defining literary phenomenon of 2025. The buzz that began with word-of-mouth is now evolving into a new story!

The official website features over 200 glowing comments from booksellers across Japan, passionate endorsements from eight celebrities, a summary manga showcasing the book's appeal, a full 50-page preview, and 'Detective Koishi's Bookshelf,' introducing the mystery novels beloved by the protagonist.

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Official Website for 'Detective Koishi Doesn't Fall in Love'

https://www.shogakukan.co.jp/pr/tanteikoishi

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Special PV for 'Detective Koishi Doesn't Fall in Love'

https://youtu.be/v3sI-OLfyUM

Endorsements

・"The inferno of reasoning that burns through the sensitive realms of Reiwa-era orthodox detective fiction. I surrender completely to the solution chapter, which feels like a deathbed vision on the verge of heartbreak.♡" —Rintaro Hōgetsu (Author)

・"Hah, I think I've figured it out!" By the time you think that, you're already trapped in the author's scheme—just as I was. —Atsuya Higashikawa (Author)

・"A beautiful fusion of a twisted, charming romance novel and a meticulously plotted orthodox mystery. It's also a literary work that portrays various forms of love, which I thoroughly enjoyed." —Yutaka Itogi (Author)

・"Tired of shallow romance and weak detective fiction? Then you won't accept this challenge. My solve rate was about 5%, I'd say." —Tatsumi Ashikawa (Author)

・"My first mystery novel ever! It taught me the joy of deduction! And then I got everything wrong!!!" —Iwakura (Comedian, Frog亭)

・"Love turns your brain inside out... Let me say this: It was amazing! Seriously, no spoilers allowed!!!" —Kamoshida Seven (Bookseller Comedian)

・"Here lies the reason we're drawn to orthodox mysteries. Novelist Mori Basil is undoubtedly in love with the mystery genre." —Kengo Kamijou (ken-go@Novel Introduction)

・"After a while, readers will realize: this book is, from beginning to end, a meticulously crafted orthodox puzzle mystery." —Wataru Wakabayashi (Literary Critic)

・"Great! I'm impressed! Flawless. I'm truly grateful someone wrote such a masterpiece." —Takuya Udagawa (Tokiwashobo Main Store)

・"This is what a novel should be! The excitement only words can deliver is right here. Welcome to the dazzling world of Mori Basil, who masterfully manipulates the reader!" —Keiko Hanchu (Kinokuniya Shinjuku Main Store)

・"Smirking, then shocked, occasionally stomping in frustration, and finally smiling. Wow, I was totally tricked! Ugh! Everyone else should get tricked too." —Kaori Hisada (Seibunkan Shoten, Nakajima-cho)

・"Solves love scandals with elegance, Detective Koishi's brilliant deductions... but of course, a Mori Basil work wouldn't end there! A storm of developments, shocking truths, and a must-reread experience. This is Mori Basil's new-genre mystery!" —Masayuki Mishima (Keibunsha Okayama Main Store)

Additionally, over 200 booksellers across Japan have flooded in with astonished reactions!

To prevent spoilers, selected comments are partially censored and published on the official website.

Synopsis of 'Detective Koishi Doesn't Fall in Love'

Koishi, head of Koishi Detective Agency and a self-proclaimed mystery otaku, dreams of elegantly solving cases like a legendary detective. In reality, 99% of his cases are infidelity or cheating investigations, and logical mystery cases never come his way. The reason he keeps taking on these love-related cases? He's pathologically skilled at them—for a certain reason.

Just as it seems he's stuck with only love cases, behind the scenes, Koishi and his counselor Renjou uncover an unexpected truth—while an unforeseen incident quietly unfolds...

Author Biography

Photo / Miya Igarashi

Mori Basil (Mori Bajiru)

Born in 1992 in Miyazaki Prefecture. Graduated from Kyushu University. In 2018, won the Excellence Award in the 23rd Sneaker Award (Autumn). In 2023, won the 30th Matsumoto Seicho Prize for 'No One Knows: Only You Know,' making his hardcover debut. In 2025, 'Detective Koishi Doesn't Fall in Love' ranked 8th in the 2026 Bookseller Award, won 1st place in the MRC Award 2025 chosen by mystery fans, and received the 2025 Miyabon Award. Other works include 'Why Is There a Corpse in the Studio!?'

Featured on Literary Portal 'Shosetsu Maru'!

Author interviews, commemorative essays, bookseller roundtables, and literary critic Wataru Wakabayashi's review are now available.

https://shosetsu-maru.com/

Publication Details

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Detective Koishi Doesn't Fall in Love

Mori Basil

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Price: ¥1,870 (tax included)

Release Date: September 18, 2025

Format: B6 size

Pages: 328

Publisher: Shogakukan

https://www.shogakukan.co.jp/pr/tanteikoishi

※When using the author photo, please credit: Photo / Miya Igarashi