Well, this is J-Novel club, I'll stick to Japanese novels lol (If I start to go for other mediums, this comment will be way too long!! (Even I'll just give up on many titles I may mention)
Well, let's start with:
Boogiepop series:
Influence of Kouhei Kadono wasn't just on LNs, but he was cited as influence to other big name authors who are quite influential themselves:
NisiOisiN
Nagaru Tanigawa
Nasu
Yuya Sato
NisiOisiN's Monogatari along with Nagaru Tanigawa's Haruhi series promoted use of Meta in LNs, not like Meta didn't exist before, you can even find meta humor in some of Osamu Tezuka's work.
And due to wave of attack on Otaku in media back then along with this renewed passion for meta, We have Oreimo. Well, it's influence in the whole non-otaku & Otaku pair is obvious (even so many LN covers make homage to the series)
NisiOisiN's Zaregoto was a huge influence.
"And Zaregoto‘s legacy is beyond anybody’s ability to write. The work has influenced many, many, many creators. Ii-chan’s narration, the strange mixture of Osamu Dazai’s protagonist in 人間失格 (No Longer Human) and JD Salinger’s Holden Caulfield in Catcher in the Rye, has infected writers — light novels and mainstream/literary — without them realizing. It is not an exaggeration to say that visual novels like Danganronpa would not exist without Zaregoto.The worldbuilding techniques that writers associate with the likes of Horizon in the Middle of Nowhere could be charted to the Zaregoto series. Its influence goes beyond the constraints of genre and literature: it may be one of the many parts that constitute what a Japanese novel can be."
-Kastel
Well, if we are on Mystery:
NisiOisiN's Zaregoto belonged to a movement called Shinhonkaku, which some may attribute its beginning to Yukito Ayatsuji's debut, The Decagon House Murders. (Same author as Another) It's available in English with an introduction by Shimada Soji (from the same movement, some of his works are available in English as well)
Well, if we are gonna mention Japanese Mystery, we gotta mention Edogawa Ranpo. (Unfortunately, I haven't read anything by him yet)
Ryuusui Seiryoin is the probably the only name I mentioned who got nothing in English. He is one of the 5 god-like authors NisiOisiN mentioned, his JDC (Japan Detectives Club) series has inspired tribute novels by authors Otaro Maijo, NisiOisin.
There are names that are too famous to be mentioned like Osamu Dazai, Natsume Soseki (You may know him either for his translation for I love you or Kokoro), Kenji Miyazawa, Ryuunosuke Akutagawa.
The Tale of Genji
It is sometimes called the world's first novel, the first modern novel, the first psychological novel or the first novel still to be considered a classic. While regarded as a masterpiece, its precise classification and influence in both the Western and Eastern canons has been a matter of debate.
Oniroku Dan.
"The most celebrated writer of popular SM novels in Japan." -Nicholas Bornoff
(Verical has semi-autobiography anthology by him)
Dan developed his own variation on S&M, but when asked if he ever acted on his S&M and bondage fantasies with his wife, Dan replied, "No way! She would beat my ass."
There are so many authors I may mention but the comment will be way too long for that!
Edit: It might be too late to say that.