Hitotose, Hirune

"The relationship between detective and assistant is not unlike romance!" Because of his natural tendency to assist others (a "helper type" personality that makes him constantly want to lend a hand), Tasuku Mitomo has always lived in the shadows. To get out of this rut, he has made it his utmost priority to "become number one." However, at the high school he transfers to, he encounters three detective girls, who turn out to be his rivals from elementary school with whom he had formed a detective club! Thus begins Tasuku's fierce battle to support the top detectives! However... these girls seem to harbor passionate feelings of a different kind...!?

(Source: Kodansha, translated)

Isshou Watashi no Joshu de Ite!

一生わたしの助手でいて!

Tsutsui, Taishi

Famous detective Syd Craft. He's solved the toughest cases and he's adored by the public, but even he has a major problem!

(Source: MANGA Plus)

Included one-shot:
Volume 3: Mangaka no Neko de Aru.
Volume 4: Bokutachi wa Benkyou ga Dekinai Tokubetsu-hen, Yosame Hakuro wa Korosenai

Syd Craft no Saishuu Suiri

Syd Craft: Love Is a Mystery

シド・クラフトの最終推理

Noramame

One day, private detective Kanako Udagawa receives a request from client Yuiko Shinonome to conduct surveillance on her fiancé. But when Detective Udagawa drops by the fortune-teller that the fiancé's been visiting on the sly, she encounters a boundlessly bubbly woman called Sakura! See the slapstick suspense unfold with this pair of polar opposites!

(Source: MANGA Plus)

Tantei to Uranaishi

The Detective & the Fortune Teller

探偵と占い師

Asagiri, Kafka

iyutani

Over a decade before the events of the manga series, a chance encounter leads professional bodyguard Yukichi Fukuzawa to begrudgingly take an arrogant boy genius named Ranpo Edogawa under his wing. Their first job brings them to a local theater on high alert after receiving a bizarre death threat-a challenge that will require both Ranpo's brains and Fukuzawa's experience. The aftermath spurs Fukuzawa to establish the Armed Detective Agency, an organization that takes on dangerous jobs even the police won't handle!

(Source: Yen Press)

Bungou Stray Dogs: Tanteisha Setsuritsu Hiwa

Bungo Stray Dogs: The Untold Origins of the Detective Agency

文豪ストレイドッグス 探偵社設立秘話

Iguchi, Kon

Nakamura, Yuuji

Crime is ever-rising, a fact that police officer Shiro Isogai lives with every day. After the brutal murder of his fiancée, Isogai has been working tirelessly to find the killer. Suddenly, a "mysterious informant" begins popping up, helping the police locate serial killers one after another. Isogai knows this could be his chance for closure and decides his only hope is to team up with this person. But when it comes time to meet the secretive ally, he's surprised to be face-to-face with a young woman, Kuroi Hinata. Teaming up with Hinata and her "sixth sense," Isogai prepares to hunt the city's deadliest criminals and find the clues he needs to catch his fiancée's killer.

(Source: Seven Seas Entertainment)

Konya mo Serial Killer to Machiawase

Tonight, I Have a Date with a Serial Killer

今夜もシリアルキラーと待ち合わせ

Takasato, Shiina

Yozorano, Udon

Amamiya Kyoudai no Antique File

雨宮兄弟の骨董事件簿〈アンティーク・ファイル〉

Onsen, Nakaya

Spontaneous fires with no cause. A mummy found in a quiet neighborhood. Sunflowers blooming in the dead of winter. Beneath each reported paranormal event, a criminal presence may be hiding in plain sight. Anan, a cat-eared demi-human cop buried in everyday cases, finds herself reluctantly partnered with Kanai—a federal agent with spiked hair, dark shades, and secrets of his own. Together, they dig into a string of bizarre cases that defy logic. What lies behind the impossible may not be ghosts, but something far more dangerous. A mismatched duo. A trail of unnatural crimes. And a truth twisted by powers beyond reason.

(Source: Kadokawa)

Genshou X: Choujou Genshou Sousaroku

Phenomenon X: Paranormal Crime Files

現象X 超常現象捜査録

Hiruzuka, Miyako

The manga centers on three girl friends who spent their youth in the high school softball club. Now in their 30s, they turn their lives around and open a detective agency in Asakusa.

(Source: ANN)

Sayonara Diamond

Goodbye, Diamond.

さよならダイヤモンド

Kotoyama

A long-awaited bonus volume that provides a look into the future of the characters after the conclusion of the beloved manga series. Kou embarks on a life of vampire hunting!

(Source: VIZ Media)

Yofukashi no Uta: Rakuen-hen

Yofukashi no Uta: The Paradise Arc

よふかしのうた－楽園編－

Hoshikawa, Shiwasu

It's been roughly one year since Chuuya Nakahara joined the Port Mafia, and he's got his sights set on an executive position. But as he makes plans to move up, a man by the name of Paul Verlaine—claiming to be his younger brother—appears and vows to assassinate everyone he cares about! Now, Chuuya must team up with Adam, a European A.I. investigator, to stop this lunatic before the storm swallows Yokohama once again...

(Source: Yen Press)

12 Manga Like Pen to Wappa to Jijitsukon