I have family that lives in Japan for 15+ years and, while being a nice country with good quality of life, they say foreigners can never expect to be fully acknowledged citizens (e.g. how difficult it's to get citizenship, requirement of Japanese ascend, etc). It seems very closed to foreigners.

Maybe that's different in the tech world.

Japanese citizenship is actually much easier to get than other wealthy countries -- if you've lived in Japan for five years on any non-tourist visa and you're willing to give up all other citizenships you hold, you're in. The thing that's so notoriously hard is permanently living in Japan without becoming a citizen, which usually requires marriage or descent.

I havnt applied yet, but I'm treated very well(better than locals in most cases).

I have yet to see any discrimination, compared to Australia where my wife(Japanese) regularly had issues.

As long as you make an attempt to respect the culture and (ideally) make some attempt to learn Japanese - I've found only the most rural areas would dare to treat you poorly. They'll treat you well and when you are out of site they'll confide in friends about the "smelly foreign pig". Without a confidant, you'd never be any the wiser. People with tattoos face a higher risk of discrimination than anyone of a foreign (non-Japanese) race in most any part of Japan.

As with any "rules", there are exceptions. But the above has been my experience (month-long travels totaling several years).

Meanwhile, the U.S has no problems yelling out racist slurs or discriminating against others quite blatantly.