Surprisingly, there have been tons of anime or manga to come out after an original video game or visual novel, but the phenomenon happens in tons of different permutations. Everyone assumes that most of the time an adaptation of manga to anime is the natural progression that the industry follows. Surprisingly enough, some of your favorite anime probably aired before the manga was even in production.
If that wasn't what happened in that particular case, there's a good chance that the manga was actually in production at the same time with the anime as a promotional tie-in. While there are a few that don't have the manga as the main work you may be familiar with like Gungrave or Pokemon, there are tons most people have no idea about. Here are a few of them now.
10 Angel Beats!
Angel Beats! is an anime developed by Aniplex and P.A. Works and is based on a story and character design by two animators who work for the visual novel developer Key. It takes place in a high school setting, with the twist being that the students attending the high school are dead and doing their best to figure out how they died and why they're there.
It focuses mostly on a boy named Otonashi, who meets a girl named Yuri who recruits him into an organization that fights against the student council president known as Angel. It received positive reviews and was praised for its music, its humor, and its action, while some complained that it's too short to include everything it wants to effectively. Since the release of the show, three different manga series have been made based on the anime.
9 Code Geass
Code Geass is an anime series produced by Sunrise and directed by Goro Taniguchi. It follows the story of LeLouch Vi Britannia, who gets a supernatural power from a woman known as C.C. He uses his newfound power to command an army of mechs against the rule of the Holy Britannian Empire.
It was well-received by critics and fans alike, selling over a million copies of physical media. It's also won tons of awards in addition to being praised for the moral questions it presents, the characters, and the narrative. The manga consists of 4 different incarnations, all covering different alternative scenarios.
8 Anohana: The Flower We Saw That Day
Anohana: The Flower We Saw That Day is an anime strangely enough created by a collective of artists who call themselves Super Peace Busters. Six middle-schoolers begin to grow apart after the death of one of their best friends.
5 years later, the leader of the group Jinta is shown having stopped going to school, not talking to friends, and generally dropping out of society to deal with the trauma induced by the incident until Meiko, the girl who died appears to him and convinces him that he needs to do everything he can to be successful again, and set her friends on the right path. There's both a novel and a manga adaptation that's been well-received, but also leaves elements out of the story.
7 Samurai Champloo
Samurai Champloo is a series that was directed by Shinichiro Watanabe, who hadn't directed another anime series since finishing the widely-acclaimed Cowboy Bebop.
It follows 3 people, a group made up of 2 samurai and a woman named Fuu. She recruits the two samurai named Mugen and Jin to search for the legendary "Samurai who smells of sunflowers". There are only 2 volumes in the manga series and while the manga was published first, the anime was finished first, meaning that the anime is the original work.
6 Dragon Ball GT
Dragon Ball GT is an anime follow-up to Dragon Ball Z, and the original author of the Dragon Ball manga really had nothing to do with it. Akira Toriyama really spent the bit of his adult life working only on Dragon Ball and didn't want to be involved with the production of GT, leading some fans to completely reject it as canon.
The plot consists of Goku being turned back into a child, and him searching for the Dragon Balls to restore himself to his actual form with his granddaughter Pan and Trunks. A manga started in 2013 which covered the final arc of the show and is starting back over at the beginning this year.
5 FLCL
FLCL is an original video animation written by Yoji Enokido that features music from a Japanese band called The Pillows, released in 2000. The story is about a young boy struggling with puberty who has his life absolutely disrupted by the alien lady Haruko Haruhara.
It was widely acclaimed and developed a cult following after it initially aired in the US on Toonami. There are two volumes of manga that have been released, featuring weird pacing and sometimes crudely-drawn passages to match the weird nature of the show.
4 Space Dandy
Another entry on this list with an anime directed by Shinichiro Watanabe, Space Dandy is a comedy sci-fi series that came out in 2014. It follows the adventures of Dandy, who's an alien hunter in space, looking for alien species that humanity has never seen before. He travels with a robot named QT and a cat friend named Meow.
The show got good reviews, noted for its unapologetically immature approach to comedy. There have been 2 tankoban volumes of manga released by Yen Press, which hit stores in 2016.
3 Kill la Kill
Kill La Kill is a series by Trigger, directed and written by a duo who had previously worked on the popular and critically acclaimed Gurren Lagann. It's about Ryuko Matoi, who's a girl on the hunt for the person who murdered her father.
She ends up in opposition to Satsuki Kiryuin, who's the student council president at the high school she attends. The manga developed for the series after it aired has 17 chapters and is licensed by Udon Entertainment.
2 Panty And Stocking With Garterbelt
Panty And Stocking With Garterbelt is a comedy series developed by Gainax that originally aired in 2010. It's oddly slightly based on Western adult animation, namely Drawn Together, with most of the ideas for the series reportedly being thought up on a vacation for the team after finishing Gurren Lagann in a drunken stupor.
The plot revolves around two sisters, Panty and Stocking, who have been kicked out of heaven for being a couple of ne'er-do-wells. The show gained critical acclaim upon release and has since been made into a manga that only has a single volume.
1 Serial Experiments Lain
Serial Experiments Lain is to this day only a cult classic of the cyberpunk genre. It's a 1998 anime animated by Triangle Staff. It was only 13 episodes but did a great job at tackling high concepts like the nature of reality, the implications of the early internet, Jungian psychology. It tells the story of Lain, a middle-schooler whose father works with an early form of the internet in this alternate timeline.
She slowly finds out that The Wired is actually a form of the collective unconscious, a Jungian concept that posits that all humans and living things are linked together psychologically, with a shared bank of concepts and ideas. The TV show has achieved tons of acclaim and been given awards, with people citing its willingness to be experimental as one of its greatest strengths. It does have a single piece of manga, which is included in one of the art books released after the series.