Not Staying True to the Mangaka's Vision
1. Tokyo Ghoul
Tokyo Ghoul, a lengthy manga by Ishida Sui, debuted in Weekly Young Jump in 2011. It officially transitioned into an anime in 2014. The narrative unfolds in a fictional world where ghouls - flesh-eating creatures - lead secret lives among humans, concealing their identities from the government.

The story of Tokyo Ghoul revolves around a college student named Kaneki Ken, who becomes a half-ghoul after an accident. Like other ghouls, Ken must consume human flesh to survive. Living as a half-ghoul, Ken must navigate between ghoul society while concealing his identity from his human friends.
Despite being considered a potentially promising product, the anime version becomes infamous for its disconnection from the manga. While the anime initially mirrors the manga, as it progresses, the storyline diverges more and more, resulting in an ending that bears no resemblance to the manga. Additionally, its second season,
2. Fullmetal Alchemist

Fullmetal Alchemist is also a prime example illustrating how anime plots can stray from manga. Fundamentally, the first half of the anime closely adheres to the manga's storyline, but from the midpoint onward, profound differences gradually emerge, especially when Ed and Al encounter their master and her lover, who also serves as a significant antagonist in the series. While many plot elements remain intact, the ending undergoes a change. This alteration brings forth a fresh appeal, but sometimes sparks controversy.
In 2009, studio Bones remade FMA under a different title, Fullmetal Alchemist: Brotherhood. Rebooting the entire series and closely following the manga's plot made many viewers feel comfortable witnessing Arakawa Hiromu's storyline fully adapted into anime.
3. Claymore

Claymore is a manga series in the action-horror genre, considered one of the best of all time, penned by author Yagi Norihiro. The story revolves around Clare, a young girl nurtured by a Yoma group after they massacred her family, with one member disguising as her brother. Joining the organization with the goal of avenging the woman Priscilla, who murdered her friend Teresa, Clare, due to her weaknesses, is ranked at the lowest level among Claymores.
When adapted into anime, Claymore does not strictly adhere to the manga's plot but rather enhances it, providing a more polished conclusion instead of leaving it open-ended. However, this ending does not sit well with fans of the manga. The anime concludes with the main character's battle against her foe, but in a way that's easier than the intense struggles depicted in the manga. This easy power-up may have completely undermined the original intent of the source material.
4. Elfen Lied

Elfen Lied stands out as one of those anime series that only adapts a fraction of the manga, yet it doesn't necessarily leave an incomplete or unfinished story. Many anime series, like Elfen Lied, understand that a story can be more captivating with a smaller episode count, focusing on the most crucial plot points.
Essentially, the anime version of Elfen Lied doesn't entirely rely on the manga. The anime consists of only 13 episodes, whereas the manga has 12 volumes and was completed before the anime's release. This indicates that the anime only adapts the early portions of the manga into episodes, omitting a lot of content. In fact, it only adapts half of the story that unfolds in the Manga. The series lacks a true conclusion, leaving viewers dissatisfied with its abrupt and incomplete narrative. Nevertheless, its adaptation into anime has garnered increased attention towards the manga.