One piece hit a new sales recod in 2020 and the popularity of both the anime and manga have been steadly increasing over the years, specialy in the west, soo wtf are you on about the sales going down? Saying demon slayer beat them in sales and thus its going down is honestly, a very missinformed oppinion, i'll tell you the reason why Demon Slayer sold soo well when the anime was airing:
The manga is shit, it has average art, nothing revolutionary or new about its story, character development is rushed and the fights are not that well done...But i will tell you what it HAS. It has an anime made by ufotable that managed to improve EVERYTHING the manga did, they made the boring fights in the manga interesting with amazing animation and the god tier sountrack and huge improvements to the pacing fixed a whole lot of problems with the story. Soo a lot of people became fans and decided to buy the manga, the thing is, since they are new fans they bough all the volumes previously released at once, resulting in a massive inflation in number of sales for that manga. You just have to look at the most recent sales numbers to realise its numbers droped a LOT.
The manga is shit, it has average art, nothing revolutionary or new about its story, character development is rushed and the fights are not that well done...But i will tell you what it HAS. It has an anime made by ufotable that managed to improve EVERYTHING the manga did, they made the boring fights in the manga interesting with amazing animation and the god tier sountrack and huge improvements to the pacing fixed a whole lot of problems with the story. Soo a lot of people became fans and decided to buy the manga, the thing is, since they are new fans they bough all the volumes previously released at once, resulting in a massive inflation in number of sales for that manga. You just have to look at the most recent sales numbers to realise its numbers droped a LOT.
If you want to talk about sales, then yes, KnY is beating OP. In ways that have never been seen before to say the least.
The most recent sales numbers are astronomical and 2 of its new volumes have easily broken OP's record for best individual volume sales in a year.
And I have no idea what new sales record you're talking about that OP apparently hit in 2020. Maybe you misread all the different headlines that referenced OP as it regularly had its records decimated by KnY , but when talking about OP's sales specifically, its physical sales are actually some of the lowest they've been in a decade.
Saying demon slayer beat them in sales and thus its going down is honestly, a very missinformed oppinion

Hmm...
