Kimetsu no Yaiba is a pleasant surprise. Though it appears to merely be another overly grim and dark series lauded for its gore, Kimetsu no Yaiba is revealed to be much more as the series progresses. Hypocrisy, mortality, hope and despair run as prevalent themes in Tanjiro's tragic journey. The myriad ways in which this journey could reach its demise run tense in the heart and the mind of the viewer, as mercy is seldom a consideration to the demons he must annihilate.
If there is one single thing to point to with Kimetsu no Yaiba, it would be its atmosphere. Brooding, oppressive, and tense are some of the adjectives I might use to describe the mood of Kimetsu no Yaiba. It is an anime that sucks you in and doesn't let you go... most of the time, anyway. It is around the tenth episode when things make an unfortunate change for mass appeal - the characters Zenitsu and Inosuke: screaming, obnoxious lunatics who you might expect to see from a series like Naruto or Bleach rather than a careful series priding itself in its atmosphere.
That's not to say that all the side characters should have been removed, or that battle shounen tropes are inherently bad. But certainly the show could have benefited from not having dude-with-boar-head yelling at the top of his lungs and some blonde dickweed whose raison d'etre is to burst your eardrums with his constant whining and crying. For one, perhaps two episodes, this is somewhat amusing and does well at giving the viewer a break from the despair, an intermission of sorts... not something you would expect from the entire story henceforth.
Although the roles of Zenitsu and Inosuke are somewhat diminished after the mansion arc, the story introduces the "Hashira" (or 'Pillars' in the localized dialogue), a set of nine warriors who sit atop the Demon Slaying corp as the strongest it has to offer. There are a few more normal faces here, particularly Tomioka, Shinobu, and Kanao (even though the latter is technically not part of the Hashira), but the rest are complete one-note gags much like Zenitsu and boar-face-man. A monk who is constantly in a state of tears, a strange woman who is infatuated with every man in existence, a constantly-angry clone of Bakugo from Hero Academia, and so on and so forth. While this might keep the interest of younger viewers and those of weaker attention spans, this contrast of silly and serious hampers the story and takes the viewer away from the atmosphere to such an extent that by the end of the anime's twenty-six episode run, it has mostly just become another battle shounen series.
But for a battle shounen series, Kimetsu no Yaiba is top of its class, and even on its own still a worthwhile endeavor. Tanjiro and his moral dilemma of having to execute demons while protecting his sister, a demon herself, and harboring feelings of sympathy for those he cuts down, makes for a far more compelling and human protagonist than almost all of his brethren. He is exceptionally weak at the start, but his two years of training make his moderate combat skills seem appropriate, and he is still vulnerable enough that no plot armor will allow him to cut down opponents regardless of their power. Even by the end, he is losing many of his battles.
Though still very much shounen in nature, these battles deserve some praise for their inclusion of wounds and injuries. Whereas most anime of this genre will have characters— especially the protagonist— being beaten half to death and still standing as if almost nothing happened, Tanjiro is repeatedly being crippled by broken bones, internal bleeding, and his body simply giving up on him. There is a limit to his vitality, and he cannot simply get up and retaliate at max power as other protagonists often do. If he is hit in the leg, his leg will break, and he will be unable to escape or to attack at full power. These are small details, but they make the story far more engaging by giving consequence to the battles and a very real potential for death and failure.
Anime set before the modern day are rare enough, but ones set in the oft-forgotten Taisho period are closer to zero. Kimetsu no Yaiba's setting is one of its greatest strengths, the early Taisho period being a bleak, short reprieve before Japan's foray into militarism - perhaps the darkest decades the country had ever experienced. Though the imperial revolution had long since hit Japan by this point, and swords were outlawed and replaced by firearms almost fifty years prior, Tanjiro and the rest of the Demon Slaying corps fighting demons rather than humans allows for melee combat to make sense in a setting where it ordinarily wouldn't. It's certainly an interesting contrast to see the characters wielding katanas in big cities where trains and primitive automobiles are thriving about, and the forlorn atmosphere of the period fits well with the tension and despair entrenched within the story.
The setting and the atmosphere are amplified by the moody and period-appropriate sound design, with the shakuhachi (Japanese flute) and other traditional instruments, as well as up-tempo Buddhist chanting permeating the music. There are occasional tracks that do not fit the setting or the tone of the show, and the opening theme should not have been a generic throwaway J-Pop song, but for the most part the music is a hit.
Which can be said for the entirety of the anime, really. It's a hit. Mostly. Had the manga been published for an older demographic, it would no doubt have been able to tell its story without the usual trappings of the battle shounen genre. But at the same time, a lesser-known publisher means the series would probably not have been published weekly or have been nearly as popular as it is, and so a studio as big as Ufotable would likely not have picked it up for a high-budget adaptation. So I can live with the realities, I suppose, and enjoy my time with the series. But I can also live without Zenitsu screaming my ears off.