With the conclusion of Vinland Saga season 2 and the 3rd season almost assuredly underway (though not confirmed quite yet), fans of the series likely have a bit of a wait in store for them if they want more of this highly-rated manga/anime series. However, that doesn't mean they don't have other options to hold them over.
There are plenty of other series out there, manga especially, that have these massive tone, storyline, or character changes between arcs, just like Vinland Saga does between seasons 1 and 2. These shifts could be a shift in the protagonist's goal, the tone of the story, the direction of the plot, or even the genre of the manga altogether. So, let's go over some of the best examples out there of manga that switch things up partway through.
8 Berserk
First up has to be one of the most iconic manga of all time, Berserk. The story of Guts AKA the Black Swordsman is one of the darkest stories in existence hands down, but it's also one of the most 'hopeful'. That said, people who only watched the Berserk: The Golden Age Arc film series are probably confused by this description, thinking something like 'Well, it's definitely violent, but it's not all that dark'. Without spoiling anything, let's just say that the Golden Age arc is just the 'tutorial' of Berserk's story.
The Black Swordsman arc that predates the Golden Age arc in the manga is only a taste test of what's to come, and that's not even including the second giant shift the series takes after the events of the Millenium Falcon arc. Overall, the series switches who the focus of the story is on, what the story is trying to say, the rules of the setting overall, and much more throughout the course of its 40+ volumes.
7 Vagabond
When people talk about the most renowned manga series of the last few decades (not including the Shonen series), there are three names that almost always pop up. Those names are Berserk, Vinland Saga, and Vagabond. And, as another coincidence, all three of these stories primarily focus on the journey of the main character from a path of pure violence (either in the pursuit of strength or revenge) to their steady growth into a more kind, empathetic, and mature human being.
And, to top all these similarities off, Vagabond even has a farming arc that massively shifts the tone of the series much in the same way Vinland Saga does. Obviously, the two arcs are incredibly different in regard to what happens, but the overall message is similar as both Mushashi and Thorfinn slowly realize over the course of their slower arcs that it takes so much strength to create life and preserve compared to just mindless killing.
6 Fire Punch
Nowadays, there aren't many anime/manga fans that aren't aware of the name Chainsaw Man. However, how many of these same fans know that Chainsaw Man's author, Tatsuki Fujimoto, had another long-running action series before Chainsaw Man by the name of Fire Punch?
While both series deal with main characters ignorant of the ways of the world, superhuman abilities, and hope in the face of overwhelming despair, they're very different stories in general. In fact, even from the first chapter alone, readers will be able to see that Fire Punch doesn't hold anything back either in a way that's entirely different from Chainsaw Man. Readers beware, this story is pretty brutal in just about every sense of the word. In any case, Fire Punch is a series that almost constantly switches its focus, its goal, and even the overall tone as long as it matches the story Fujimoto currently wants to tell.
5 Reborn
This next recommendation works a bit better as an anime recommendation than a manga one, granted, but if people read Reborn (also known as Katekyo Hitman Reborn) instead of watching it, they can get through the controversial 'slow start' of this series all the faster.
Essentially, at first, Reborn seems like it's going to be a very shallow, by-the-books shonen/gag comedy series with cute mascot characters and a formulaic story structure. However, not long after it starts (about 20 episodes or 63 chapters) the series completely commits to being a shonen series and improves rapidly. It needs to be said that this series focuses on a middle-schooler being the boss of a mafia family and being trained to use supernatural powers by the best hitman in the world...who is also a baby, so it's a very ridiculous concept. However, in spite of all that, once the story establishes the power system, the scale of the world, and the main cast of characters, the fights and story itself are pretty enjoyable.
4 Promised Neverland
In this current day and age, there aren't many people who know the named Promised Neverland who also aren't aware of its first big twist, but for the few who don't, this is another great read that switches things up a few times in some major ways.
The way Promised Neverland handles dramatic tension, people cleverly outsmarting each other, and that expression of horrified understanding on their faces when they realize they've been tricked, incredibly well compared to other manga in the same genre, so it's a great recommendation all around.
3 Delicious In Dungeon
With the Netflix anime adaptation of Dungeon Meshi in production (at the time of writing this), it seems like an apt time to talk about this manga. Not only does this manga have one of the most memorable art styles out there and one of the most creatively written fantasy settings, but it's also just hilarious.
This is primarily a cooking/comedy manga with a side of dungeon exploration. But, as the series continues, the dungeon exploration becomes more and more of a central part of the story, more characters and concepts are introduced, and the mystery surrounding the dungeon and its circumstances are steadily revealed.
2 Helck
Helck is a manga that is essentially a version of One-Punch Man where things somehow get even darker. They're both comedy series about a way-too-strong protagonist against odds that seem impossible to overcome from every angle. But, in Helck, the darker aspects of the story, when they're introduced (pretty suddenly, by the way), are much more horrifying than One Punch Man's darkest moments could ever hope to be. Individual human cruelty is often more horrifying than massive unfeeling destruction, after all.
Not to say that it's a competition between the two series, just to say that Helck somehow manages to suddenly introduce some pretty heavy concepts and story beats multiple times throughout it and yet still manages to succeed as a comedy series at the same time.
1 The World After The End
Capping things off with a manwha inclusion, it's The World After the End. This is a manwha/webtoon adaptation of the fantasy web novel from the author Sing Shong (actually a married couple under one pseudonym), who is most well-known for their series Omniscient Reader's Viewpoint. Not only that but this series is also backed by Redice Studios, who have helped put out other amazing works such as Solo Leveling and Overgeared.
In any case, The World After the End switches things up relatively early on, as the series originally seems like it's going to be one man's lonely journey up a tower that everyone else has already abandoned. But, not far into the chapters, there's a big twist and the story changes in a major way in just about every sense of the word. And, after that big switch, there are many little shifts in story, tone, or the setting that constantly keep the reader feeling like they're just starting to understand the world this takes place in.