The greatest manga may not need to be animated to prove its greatness. Some series remain unpublished because they are too ambitious or perfect. Studios hesitate, budgets fall short, and artists refuse to adapt. The reasons for the lack of animation may differ, but ultimately, these series remain in published form, saved in ink and paper, without being turned into animation.
Printed-only masterpieces hold a unique status in otaku culture. They have sold millions of copies, received multiple awards from critics, and users have built shrines to their favourite panels. Yet, there is no opening theme, no voice actors, or streaming services to host their episodes.
Greatest manga without an anime adaptation
1. Yotsuba&!

Kiyohiko Azuma creates slice-of-life manga about a curious young girl named Yotsuba and her daily adventures. Through simple yet profound storytelling, Yotsuba fosters a sense of childlike wonder in the reader.
Since its inception in 2003, the manga has developed into a cultural phenomenon. Azuma has said he thinks Yotsuba is "too normal" to have an animated version, as the "zen-like" atmosphere and the timing of the humour would be difficult to translate to film. Despite fan requests for an animated Yotsuba, the manga remains one of the best manga without an adaptation.
2. Real

Takehiko Inoue, author of Slam Dunk, wrote another sports manga based on basketball but with much greater emotional depth. Real revolves around three young men with physical and emotional disabilities who play wheelchair basketball and explores the challenges they face through each of their stories.
Unlike Slam Dunk, Real does not yet have an anime adaptation; the complexity of the subject matter and juxtaposition between real disabilities and Inoue's extremely detailed and well-developed characters make it a difficult story to properly animate. As a result, it is one of the greatest manga works still awaiting a legitimate adaptation.
3. A Bride's Story

Kaoru Mori's historical manga takes place along the Silk Road, back in 19th-century Central Asia. The story focuses on a girl named Amir, 20, who is married to a 12-year-old boy, Karluk, in an arranged marriage. Even though the giant age difference may ruffle some people's feathers, the series presents its characters with dignity and consideration for culture.
The manga features great detail in both historical fact and illustration, and has received numerous critical accolades. The amount of detail in this manga would be hard to duplicate by any animation studio due to budget and capabilities. This is definitely one of the greatest manga series that is deserving of a lot more credit.
4. Goodnight Punpun

Inio Asano's psychological masterpiece follows Onodera Punpun from childhood through adulthood. The protagonist appears as a simplistic bird drawing, while other characters receive realistic illustrations. This unique artistic choice reflects Punpun's internal struggles and emotional detachment.
Given its experimental visual style, it would be very hard to animate it in the same manner. Since Punpun's dialogue is quite low, voice-over casting would be even more difficult. It is considered by many to be one of the greatest manga that should stay as a print publication.
5. 20th Century Boys

Naoki Urasawa's massive mystery/thriller novel spans thirty years. It follows childhood friends as they confront a doomsday cult. The mysterious leader (nicknamed "Friend") has some type of knowledge concerning aspects of their childhood imaginations. In order to stop the devastation of the planet, they need to reassemble all their forgotten memories.
Urasawa's deep and layered plot and story would require a very large number of episodes to animate. The manga has received many awards, including the Kodansha Manga Award. It is one of the greatest manga in history and is in dire need of an animated adaptation.
6. Fire Punch

Before he printed Chainsaw Man, Tatsuki Fujimoto was telling this violent story featuring Agni, cursed with unquenchable fire on his regenerating torso. He seeks vengeance on the people responsible for destroying his village, and he walks through an icy post-apocalyptic environment.
Tatsuki Fujimoto has a lot of imagination and demonstrates it very well through Fire Punch. Chainsaw Man is highly rated for its animation. However, Fire Punch has never been animated. Fire Punch would rank among many other greatest manga as one of the best that have been picked up by a studio and produced as an anime.
7. Pokémon Adventures

The Pokémon manga has been around for almost thirty years and has had multiple arcs and different main characters, all based on characters from the Pokémon video games, with some more mature things (like ashes of Pokémon, for example), plus some darker narratives.
The manga has been around since 1997 and has tons of material for production, but having an already existing Pokémon Anime that has been successful means no financial incentive to animate this version, even though there is a huge fanbase behind it. Pokémon Adventures is one of the greatest manga to never get animated.
8. Satoko and Nada

Yupechika's heartwarming manga series follows the experiences and thoughts of two college students, Satoko from Japan and Nada from Saudi Arabia. The two of them experience American culture while sharing their own perspectives, which helps promote cross-cultural understanding between people of different cultures through humorous means and through each other as friends.
By both being educational and entertaining, the series uses a unique way of relating to a wide variety of readers. Although it is only four volumes long, this series is certainly worth animating, probably one of the greatest manga ever made, to promote worldwide understanding.
9. Lone Wolf and Cub

The Japanese comic book series by Kazuo Koike and Goseki Kojima was first published in 1970, telling the tragic story of Ittō Ogami, a man wrongfully accused of being an assassin. He goes on a quest for vengeance with his infant son Daigorō as they travel across Japan together as a wandering executioner. The series changed the way that comics are written and drawn.
Although the series has had films made about it and is well-known for its iconic status, there are no traditional anime adaptations of this series. The historical context in which the story takes place, as well as its profound philosophical aspects, would make for great animated adaptations. This is arguably one of the greatest manga from the golden age.
10. Vagabond

Takehiko Inoue’s masterwork portrays legendary swordsman Miyamoto Musashi’s path toward becoming enlightened. The story is derived from the novel of the same name by Eiji Yoshikawa, but takes what was once considered "samurai fiction" and turns it into a philosophical meditation.
The stunning artwork in Vagabond establishes standards few animated productions could hope to attain. The extraordinary detail of Inoue's brushwork and compositional skill is so refined as to produce panels that could be displayed in a museum. This philosophical epic represents the greatest manga that may never receive animation, preserving its artistic purity in print form where it truly belongs.
The greatest manga on this list share one thing: They terrify studios. Vagabond's brushstrokes can't be replicated on a TV budget. Punpun's visual language breaks every animation rule. Lone Wolf and Cub doesn't need another medium when it already perfected one.