This article is laughably wrong (probably a puff piece to entice Korean students to work in Japan). The truth is exactly the opposite: there are fewer Koreans in Japan every year (as measured by foreign residents in Japan -- this includes work and student visas). The fastest rising immigrants to Japan from 2015-2018 are in descending order[1]:

Vietnam Cambodia Uzbekistan Myanmar Sri Lanka

South Korea comes in dead last, having DECLINED by 10% during the same period.

The truth is that as soon as Korea became a developed country, having joined the OECD in the 90s, immigration to Japan slowed to a trickle, precisely for the historical reasons that you might suspect.

[1] https://en.wikipedia.org/wiki/Demographics_of_Japan#Foreign_...