NISIO, ISIN

Demizu, Posuka

The spin-off stars an adult B.T., who is employed at Dinosaur Hotel in Las Vegas as a magician. After watching B.T.'s magic show, Koichi Mugikari learns that B.T. is actually employed for helping the hotel's casino handle gamblers who have unusual winning streaks. 

(Source: JoJo Wiki)

Makouseinen B.T.: "Busou Smoker" Jiken

Cool Shock Guy B.T.

魔好青年ビーティー「武装スモーカー」事件

Umiharu

The manga is set in a certain "eastern country," where the commerce and use of an illegal drug named UDL has spread widely following the end of a devastatingly long war. Here, a boy named Ibuki is searching for his long-lost mother. One day, he meets a mysterious girl named Mylphy, and Ibuki's search for his mother will begin to take on a surprising twist.

(Source: ANN)

Bloodict

ブラディクト

Minenami, Ryou

High schooler Miko, who thought he'd be inheriting his grandfather's mountain, has lost his crush to his friend and is at the bottom of his school's hierarchy. His one solace was the mountain, but now a mysterious masked man is building a small cabin there... Tagline: Am I weak? A tale of love and hate spiraling around a mountain.

(Source: MANGA Plus)

Sangeki

Haunted Peak

山劇

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!

Omori, Fujino

Yuunagi

Will and his childhood friend Elfaria enroll at Regarden Magical Academy, each with their own challenges to overcome. Even among the incredible mages at the academy, Elfaria quickly shows her talents and is scouted to join the Tower, the group at the very heart of magical society. Will, on the other hand, considers himself talentless and falls into despair...but in that despair, he draws a blade. In a world of wands run by the Magia Vander, one young boy alone wields a sword!

(Source: Yen Press)

Tsue to Tsurugi no Wistoria Grimo Acta: Hajimari no Namida

Wistoria's Wand and Sword Grimo Acta

杖と剣のウィストリア グリモアクタ ―始まりの涙―

Baek, Nara

Oscar

A thirst for revenge drags Raymond into a sinister game at his new boarding school, as he finds himself the mouse within a dorm of twisted cats who wish to devour and defile him in the worst ways imaginable.

(Source: Tappytoon)

The Bad Life

불우한 삶

Shimotsuki, Seira

Mariya is one of the students about to begin attending Graad Academy. However, during the entrance ceremony, she witnesses an attack by a group of dreadful warriors that seem to be out of this world. When the situation descends into chaos, a mysterious and unexpected ally appears to stand in her defense...

Saint Mariya

聖闘士真理矢

Abe, Akiko

Chino, Haruka

Kazuki Tsukigase is a high school boy who carries a certain secret. In search of a place where no one knows him, he enrolls at Sakijima High School on a remote island.

On Sakijima, there is a place known as the "Cove of Spiriting Away." One early summer day, Kazuki finds a girl lying unconscious in the cove. The girl—Nanao, 16 years old—later regains consciousness in the hospital, but her identity remains unknown. What is the meaning behind the word "1974" that she murmured?

A touching boy-meets-girl story.

(Source: MAL News)

Doko yori mo Tooi Basho ni Iru Kimi e

どこよりも遠い場所にいる君へ

Tanio, Gin

Mikanbako

Yurukowa! Muteki no JK ga Shinrei Spot ni Totsu shimakuru

Yurukowa! An Invincible Girl Attacks a Haunted Spot

ゆるコワ! 無敵のJKが心霊スポットに凸しまくる

Sugii, Hikaru

Pirates Cat

Tenjou Tenge Seitokai Prifaes

天嬢天華生徒会プリフェイズ

Yonezawa, Honobu

Sagawa, Anri

Kobato is a high school freshman who wants to live a normal life, not become a great detective. He tries to lead a quiet and modest school life with his like-minded friend, Osanai, but one mystery after another keeps coming his way. Even though he doesn't want to stand out, Kobato is compelled to solve mysteries. Will he ever find peace?

(Source: Kodansha, translated)

12 Manga Like Koten-bu Series