I don't know where you are getting your information that the population of Japan is still growing. Japan's population is already declining.
http://www.stat.go.jp/english/data/handbook/pdf/2017all.pdf "Statistical Handbook of Japan" Table 2.2
https://www.populationpyramid.net/japan/2020/ ( https://www.populationpyramid.net/sources )
https://www.worldometers.info/demographics/japan-demographic...
https://qz.com/1295721/the-japanese-population-is-shrinking-...
https://www.nippon.com/en/japan-data/h00705/ "Japan’s Population Falls for Ninth Straight Year"
https://www.ft.com/content/29d594fa-5cf2-11e9-9dde-7aedca0a0... "Japan’s population decline accelerates despite record immigration"
Even your link confirms that the population is in decline, just not as quicky as some reporters say.
"While the fertility rate declined from 4.32 in 1949 to a low of 1.26 in 2005, the total population was increasing >>until 2011<< "
"Japan’s Population Decline Not as Rapid as Media Portrays".
I just noticed I could replace 2017 with 2019 in the official statistics link and did so, resulting in http://www.stat.go.jp/english/data/handbook/pdf/2019all.pdf
It is the same Table 2.2 That still shows a decline and projected decline.
I am not seeing anything that backs up your assertion that
> birthrate of Japan is considered low, but they are growing still
If you still want to assert this as fact then you are going to have to provide a reason that the Japanese government's own statistics and projections over at least the last 5 or so years are incorrect and what should be used as authoritative data instead.