Japan doesn't have UBI, but it's welfare system is extremely expansive as Article 25 of the Constitution guarantees a minimum standard of living through livelihood, housing, education, and medical assistance.

Additonally, Japan has spent decades thinking about this eventuality (at least since the 1970s), which is why Japan worked on the "Flying Geese" paradigm where Japanese public-private ventures would end up become major capital stake holders across Asia, the US, and Europe.

How so? Why would I work harder, If it's all going to pay for someone to sit and do nothing?

After entire generations are subsidized by ubi, the system will collapse on itself.

In the US, native tribes get ubi when they turn 18. The end result isn't happiness or prosperity.