Berserk
Berserk is a manga written and illustrated by Miura Kentaro. It has seen two anime adaptations of the same name.
The series follows the adventures of the protagonist Guts, who does battle against the forces of darkness with a really, REALLY big sword. In fact, it's probably the only anime/manga in existence where the other characters actually notice that someone's sword is unrealistically large, often pointing out "Fuck me, that's a big swoOH GOD IT CUT ME IN HALF BLARGH". It is, in fact, so large that it cannot actually be used while mounted because swinging it makes the horse fall over. Guts himself can only use it by virtue of training with oversized swords since he was a small child, in combination with his titanic (and possibly supernatural) strength.
Chronologically, the story's beginnings are simple gritty medieval violence, following the exploits of a band of mercenaries as they make a name for themselves in the world and acquire power and glory. It swiftly descends into oh-god-what-the-fuck horror when evil deities and their monstrous "apostles" get in on the action, and via a roundabout series of events Guts ends up hunting down his old companion now ascended to godhood, determined to get revenge for his betrayal. It is all magnificently grimdark.
Just to add to the grimdarkness he has a waifu that got raped by his best friend that turned into a demon. His waifu then had a miscarriage from all the trauma and his kid's fetus comes back to haunt him every day. Later in the series his kid comes back looking about the age of 3-8 years old and saves him and his friends by using terrifyingly effective abilities on par with lofn. Then said kid disappears again leaving a puzzled Guts and a slightly distressed but still insane waifu.
The series has a massive following both in Japan and in the west and has been running for almost two decades. The author, Miura, is well known for taking extended breaks from production, and given his advancing age and his recent statement that he considers the series about one-third complete, has led to fears by many that he will kick the bucket long before he actually finishes the series.
According to some fa/tg/uys Guts is one of the lost Primarchs. Some actually speculate that Guts is Angron's son. Or even Angron himself back in the day or some shit.
/tg/ greatly enjoys it because it's essentially a fucked-up mix of WARMACHINE and D&D 3.5.
trolling
The author, having realized it's too boring to continue the story with only Guts, his tinkle fairy and his mental ill waifu, decided to "soften" up the manga a little bit by introducing a loli witch name Schierke and another tinkle fairy from Peter Pan. This causes rage among the fanbase, since they believe Berserk is no longer about a manly, badass mercenary with his vengeance against his homo-looking former comrade, but instead adding side stories about the loli and the shota, even making Schierke naked in front of Guts for some fan service. But since we have seen burning dead children shove each other's asshole with their bee hive and countless of rape and Casca tentacle porn, we can say the author is also a rule 34 fanboy. Besides, it's not like Guts lost his manliness anyway, since he still the only one who gets shit done most of the time.