Hi , I know you are gathering information. So let me just put some examples for your reference.
Friend 1: Got a Naturalization in Less Than 8 years.
She graduated in a Japanese University with a degree of Computer Science/Engineering.
Worked in a Japanese Company afterwards.
JLPT level1.
Proficient in both written and reading Japanese.
Married to a Japanese and have a kid with him.
She got her Visa because of her skill.
Self-sufficient.
Friend 2: Got a PR for more than 30years of Living in Japan
She got married to Japanese and had a kid with him.
Spousal visa all the time.
Can speak Japanese but not on a business level.
Can barely write and read Japanese.
Pass JLPT 2 before applying for PR visa.
Worked Part-Time most of the time.
Both friends were married to Japanese nationals, so it shortens the time requirement. But other than that it all comes down to skills and your contribution to the country.
Personally , I have been in Japan for 7 years now and have an Engineer Visa. I usually get 1 or 3 years visa and the re-entry permit has the same span as my visa and I never had any problem with that.
Anyways, my case is not the same as yours.
Of course, there are also issues regarding the countries culture.. etc but I supposed you have already thought about them.
Anyways, good luck
