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Jinrui Saikyou no Hatsukoi

人類最強の初恋
Сайкё

Main Story

novel
and 1 more
A dropout from an elite Houston-based program for teens is on a visit to a private island. Its mistress, virtually marooned there, surrounds herself with geniuses, especially of the young and female kind—one of whom ends up headless one fine morning. 

(Source: Kodansha USA)

Sequel

novel
The second instalment of the Saikyou Series. 

Aiming for 10,000 metres depth in the deep sea! 

Together with the genius psychologist Jikumoto Miyori, Aikawa Jun—a contractor—heads to the bottom of the sea in pursuit of a missing treasure ship and research team. As soon as they arrive, they are besieged by a school of man-eating fish! 

(Source: Kodansha, translated)

Other

manga
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)

Other

novel
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