You guys are all correct, but you guys forgot about one very important thing:
demon slayer is about bunch of kids with "SAMURAI" swords fighting demons. Anything with
SAMURAI swords and
demons is automatically popular. Bleach made a success out of it, or look at Zoro for example?
Nami originally was supposed to be Luffy's vice captain (her name was battle axe Nami) but someone very close to Oda recommended him to change her with a
SAMURAI themed guy who has some
DEMONIC powers for marketing purposes.
And sure that worked like a charm!!! Zoro fans are now 50% of the entire one piece audience, there are a lot of people who read one piece
SPECIFICALLY for Zoro. If Zoro didn't exist in the story and Oda didn't make that
KEY decision, then one piece wouldn't be nearly as popular as it is today. Maybe we should all be thankful to Zoro for that? 🤔 anyway, you get the point. Demon slayer is popular because it has the most popular
THEMES in it:
SAMURAIS, SWORDS, DEMONS, FIER POWER ETC.
Black Clover's author tried to pull the same shit with the same themes, but he did it wrong, plus Black Clover doesn't have the animation that demon slayer has.