Series which have fallen of the most after a promising start

[RavenSupreme]

The worst I can think of is "The Constellation that returned from Hell".

Which had an incredible first arc in outer space as the protagonist actually progressed towards and became a legitimate stellar constellation.

Only to then devolve into the epitome of boring generic isekai-chliche upon returning on earth.

 

[Qinglong]

Re Life player MC returning back to before the apocalypse promising to make things better then does nothing for years and ends up a literal dog to primary school children

 

[RavenSupreme]

Re Life player MC returning back to before the apocalypse promising to make things better then does nothing for years and ends up a literal dog to primary school children

Oh damn yes I recall that I think. I thought that the entire primary school thing is going to be the usual one/two chapter arc before the skip but it became the literal story. And whats worse he even behaved like a primary schooler himself, despite having the full brain capacity like an adult. Mad creepy.

 

[OtherGalaxy]

the seven deadly sins, although 'promising start' might be generous depending on who you ask. i really don't think the first 100 chapters were bad though, but that last 200 was the worst I've ever experienced in a manga

 

[B Rabbit]

Toriko.

Not saying it was bad, but the rushed ending and GW left alot to be desired.

 

[OtherGalaxy]

Toriko.

Not saying it was bad, but the rushed ending and GW left alot to be desired.

neo is one of the scariest villains in shounen and giving him a "he just needed someone to share food with him :D" happy ending was sooooo bad god

great fights and concepts but what a fumble at the end there

 

[Darth Nihilus]

Fairy Tail comes to mind

 

[Dwimmerlaik]

Vinland Saga was one of my favorites, but I've basically dropped it now. While I don't think it's terrible in its current state, it definitely fell off hard as far as I'm concerned.

 

[Yoshi]

Attack On Titan. Part I was literally incredible, then it deteriorated in quality during Part II by such a strong amount. People say the ending was bad but all of Part II was really, and it just kept getting worse. By the time the Rumbling started there was no saving it.