Not sure what this dude is on, but he clearly doesn't know anything about the Japanese legal system.
Not going to go through the whole thing, but there is legal recourse for every point he brings up.
Sounds to me like someone who didn't know he should talk to a lawyer in early days and let some doors get closed, and is now bitter.
Lesson to be learned - if you think things are going south, talk to a lawyer. If you are presented with something to be signed or stamped, talk to a lawyer.
Consultations are available at the bar association for 5,000 yen. No excuse to not avail yourself.