Although manga creator Tsutomu Nihei is well-renowned for his sprawling sci-fi epics Blame! and Knights of Sidonia, with these further volumes of Tower Dungeon, he proves he's equally adept at creating fascinating, mysterious fantasy worlds. In place of biomechanical monstrosities, he draws utterly terrifying basilisks, creepy slugs that reanimate the dead, and cannibalistic human/dragon hybrids who think nothing of devouring their enemies. The world in which Yuva and his party must attempt to survive is a perilous one, full of hidden dangers and scheming adversaries.

In my review of the first volume last year, one of my few criticisms was that the story seemed overly simplistic. Nihei quickly remedies that by introducing a great many new characters and factions. In fact, the fourth volume barely features Yuva and his allies at all, instead introducing an entirely new group of characters who only integrate themselves with the core cast in the final pages. It's just as well the new guys are an entertainingly eccentric bunch, including a half-dragon scholar whose draconic right eye bulges like he's wearing a permanent monocle, a cute, oversized mouse warrior lady, and a dwarf-like guy who rides an animal that's a cross between goat and crow.

Yuva's progress up the tower is a case of two steps forward and one step back, as unspeakable horrors lurk behind many corners. Nihei's Dragon Tower is a lot like Akihito Tsukushi's Abyss (from Made in Abyss), except inverted. The higher our heroes climb, the weirder and more dangerous the threats they must face, and the Tower's true nature is one of the series' central mysteries. No one knows who built it, and no one has ever reached the top. At three kilometers wide and 1800 floors tall, it certainly counts as one of those Big Dumb Objects (BDOs) beloved of fantasy and science fiction. Nihei in particular loves BDOs – the interstellar Sidonia starship certainly counts as one, though Blame!'s solar system-wide City is even more mind-bogglingly enormous.

Nihei uses his skill for depicting weird architecture to show his characters traversing varied challenging landscapes – from impossibly high, crumbling spiral staircases to wide open Great Halls supported by colossal pillars, the Tower is never boring to look at. Everything he draws looks suitably old, weathered, and pleasingly analog. As usual for Nihei, his monster designs are truly bizarre, gooey, and organic. The aforementioned basilisks, who turn an entire army of men to stone before shattering them to pieces, are almost butterfly-like with their huge wings, upon which are emblazoned fake, staring eye patterns. They're likely to show up in my nightmares.

Characters aren't always Nihei's strong point, and in some of his other works, it can be hard to tell individuals apart. He seems to have taken this criticism on board for Tower Dungeon, for most of the characters have wildly different builds and features. I especially like Lilicen, but then I've always had a soft spot for good old-fashioned fiery tsunderes. Gradually, Yuva endears himself to her – not only by bravely saving her life on more than one occasion, but with his endearing straightforwardness and obvious care for his party members. The scene where they both wear rings that allow them to hear each other's thoughts is both hilarious and sweet. Yuva grows a lot over these volumes, demonstrating his innate heroism and stoic determination to succeed, even if he's still young and inexperienced. Some hints about his secret origins mark him out as a fairly typical fantasy protagonist, but that's absolutely fine in context. There's so much other freakishly weird shit going on in the background here that a little tropey-ness is completely forgivable.

Even supporting characters are extremely compelling, especially the hairbun-wearing female leader of the Excavation Guild who takes a shine to Yuva when she witnesses his freakish strength. If I were in his place, I'd be sorely tempted to forget about the damned princess and get with the hot, scary excavator lady. Thankfully for everyone else, Yuva is not like me. The other notable supporting character is secondary antagonist Carache, an amoral dragon-guy who slurps and chews his way through a large number of extras. Whereas the Necromancer remains something of an enigma, Carache is a proper boo-hiss villain whom I'm sure will return to play havoc with the main cast later in the story.

What really sets Tower Dungeon apart is the ever-present sense of progression, of uncovering the unknown, of overcoming trials to progress further. These are the elements that make dungeon-crawling RPGs so compelling, and Nihei nails them. Who knows what abominations await Yuva and his part as they continue to ascend into the mysterious heights, but I fully intend to join them all the way to the end.