Line is the biggest messaging (and taxi, and many other things) app in Japan, Taiwan and Thailand.
The software Samsung puts on their phones may just be a layer on top of Android but is still very influential by being run on billions of end-user devices.
The country's definitely low on internationally impactful SaaS, though they do exist e.g. Sendbird and Moloco.
Line was previously owned by Naver, but is now Japanese-owned. I believe it was actually developed in Japan - it happened as a reaction to communication problems during the 2011 earthquake/tsunami/nuclear disaster. It's an absolutely excellent app, no ads or anything, only pure communication with everything you would want for that purpose.
LY Corp is owned 50/50 by Naver and Softbank. It started as a reskin of Naver Talk, and the product development has effectively been done in Korea throughout the years. They've intentionally marketed it as being a Japanese app/company to assauge the Japanese government, as unlike in the West, East-Asian governments understand that an app that the entire nation has come to rely is a critical piece of infra that needs to be in national hands. But this has not reflected the reality.
This strategy of pretending to be a Japanese app has worked for a decade but now seems to be coming to an end, with the JP government looking to force Softbank to somehow broker a deal with Naver to reduce their share to less than 50%.
This is completely false. Line has been developed almost entirely in japan after the first couple years. The japanese team at this point is a couple orders of magnitude larger than the korean one, and most of the development is decided in japan.
These people aren't being hired to pick their nose [1]. Nor is it like the US where they only place such adverts to justify H1Bs.
There has been an entire scandal about Line's data having been hosted in Korea all this time for more than a decade, after which the servers finally got moved to Japan. You're hardly going to place all physical servers in country A and then do all backend and infra development in country B.
The software Samsung puts on their phones may just be a layer on top of Android but is still very influential by being run on billions of end-user devices.
The country's definitely low on internationally impactful SaaS, though they do exist e.g. Sendbird and Moloco.