So, looking the situation over, I have a fair number of potential reasons for Samurai 8's under-performance. Feel free to agree or disagree on any of them:
1. Overpromotion
This was perhaps the biggest immediate thing for many people, and it does bear repeating, Samurai 8 was pushed way too hard for its own good. While obviously the news of Kishimoto's return is a big deal and deserves to be publicized, they really should've just stopped at the promo video at Jump Festa. All the advertising via billboards, pamphlets and interviews was overkill, and created this dangerous idea that Samurai 8 was going to be much more epic than it actually was. Remember, this is an industry where almost nothing is advertised before it begins running, Samurai 8 getting so much was bound to raise eyebrows.
2. Timing of the Release Date
This was just stupid, honestly. Why did Shueisha even think this was a good idea? One Piece, one of the benchmark titles of the Modern Era, a series which utterly exploded in popularity this year, the two biggest new series of the year, a couple of well-established titles, and the concluding volume to a well beloved series. Why on Earth did they think that trying to sell two volumes of Samurai 8 was going to work? They didn't even advertise it well, giving no promotion for it in Jump or online, and instead betting on a crappy pamphlet strategy which was just intrusive advertising.
3. Too Much of a Passion Project, Not Enough Market Appeal
Kishi clearly has a lot of big ambitions with Samurai 8, but so much of them is built out of his personal interests like Star Wars, rather than anything which would directly appeal to a modern Japanese youth audience. The result is that we have a manga set in a vague and rather unrelatable setting with a hazy but "epic" story, with incredibly heavy amounts of terminology and info-dumping. He really should've done some market research, but, since S8 is a project where Kishi was given the ability to do whatever with no editorial interference, no such mandate was given to him.
4. An Inability To Compete
This is the most subjective, but I think the issue a lot have with Samurai 8 is that it's...okay. Compared to the modern battle manga, it's not solid and powerful like MHA, lacks BC's strong cast and setting, isn't deeply emotionally resonate like Kimetsu, and isn't exhilarating and thematically complex like Jujutsu. It's...a bog-standard battle manga, one which might've looked cool a decade ago, but now looks outdated and kinda choppy. This, again, is where some editorial guidence could've helped a lot, but instead, Kishi just kept to his own little world.
5. A Lack of the Real Target Demographic
This is pretty speculative I'd admit, but I think S8's first and biggest misstep is that Kishi intended the series for a younger demographic that really isn't there nowadays, per survey data. Samurai 8 kinda reads to me like a manga he thought his son would enjoy, you can infer as much if you read the interviews he did before the series started, but that kind of style isn't exactly going to be a big hit when the people it appeals to are in the minority of magazine and especially volume readers. To the majority, Samurai 8 just looks...kinda half-baked, to be honest.
So, those are the main reasons, I think. Feel free to debate them, I'm sure someone has a good counterargument to mine.
