Kimi to Boku no Kowareta Sekai

The second installment of the Sekai Series. 

The music room in the second semester at Kazusaen Middle School, where the clock tower is not repaired. The relationship between Byouinzaka Meiro and Kushinaka Choushi began there. The school's three eccentrics, Kushinaka Kogushi, Douno Kurori, and Gakemura Rouya, maintain a distorted balance. And then a murder occurs. The search for the culprit begins, with Meiro and Choushi playing detective, and the collapsed balance is further shattered... 

(Source: Kodansha, translated)

What if Monogatari's Ararararagi, Zaregoto's Ii and Jun "Humanity's Strongest" Aikawa, and Okitegami Kyouko no Bibouroku's titular forgetful detective all attended school together? In 2002, NisiOisiN won a Mephisto Prize prize for his debut novel Zaregoto, Book 1: The Kubikiri Cycle. Part of the 15th anniversary celebration will be 4-panel crossover gag manga Seishun Kijin-den! 240 Gakuen (240 is a pronunciation pun - 240 can be read as "Nishio," so "Youth Oddball Story! Nisio Academy").

(Source: Crunchyroll)

A series of crossover stories between characters from Monogatari and characters from Nisio's other works. Originally, 4 crossover short stories were released during the theatrical screenings of each Kizumonogatari movie. The stories were bundled up into Mazemonogatari, and included 3 unreleased stories.

Includes 15 stories:
Kyouko Balance
Jun Build
Nomi Rule
Mayumi Red Eye
Kuroneko Bed
Risuka Blood
Hitei Clear
Iori Fugue
Shiogi Ranger
Akari Triple
Rizumu Rock 'N'
Mikoko Community
Kuu Invisible
Rai Roulette
Magakoro Finisher