So I know this is just adding to the kimetsu insanity but I feel like this is something worth pointing out.
These are kimetsu's 2 novels in Oricon's 2019 yearly chart (respectively 3rd and 4th):
Kimetsu no yaiba - shiawase no hana - 210,966
Kimetsu no yaiba - Katahane no chou - 196,674
And these are them now
Kimetsu no yaiba - shiawase no hana - 426,779 ( + 215,813 in 2020 ) *
Kimetsu no yaiba - Katahane no chou - 420,192 ( +223,518 in 2020 )
For context, this would already put Katahane no Chou as a close 2nd on 2019's chart and a close 1st on 2018's chart, only considering 2020's sales. Those 2 novels are still selling above 20k weekly (about 25k each as of last week).
The most sold light novels in the past few years were:
2017 : your name - 316,193
2018: Overlord 13 - 240,361
2019 : Weathering With You - 511,159
So tl;dr Kimetsu is not only poised win in the manga categories but is also a very strong contender for most sold novel volume and series (both of which are going to be pretty much a lock if it releases a third light novel).
So uh...yeah.
*fixed thanks to Ryuusei