Japan is peculiar in the sense that in no other major market for console gaming one publisher, which is also a platform holder, own such a huge market share in term of software sales compared to all the other publishers combined.
In 2020 Nintendo+Pokemon Co. were responsible for more than 50% of the physical software sales in Japan, it's absurd.
This is a combination of two opposing trend: Nintendo's software sales holding strong and third-party software sales declining over time.
In truth since the console market went mainstream in Japan with the Famicom, Nintendo was almost every year the number one publisher there.
It's no coincidence that almost all of the top 20 best selling console games ever in Japan are published by Nintendo (or Pokemon Co. which is controlled by Nintendo).
Top 20 best selling console games in Japan (sell-in; miss Minecraft which with all the various version combined should be around 5M, also note that while the chart combines Pokemon Red, Green with Blue the original release in Japan in 1996 was only formed by Pokemon Red/Green which sold-in 8.22M)