https://en.wikipedia.org/wiki/File_sharing_in_Japan
Oddly, Wikipedia is less clear on if anybody has been convicted, but being arrested is already sufficiently career-destroying (weeks in jail for interrogation etc).
The public messaging also seems to be more serious than what I typically see in the US. For example, I feel like anti-piracy announcements play more consistently in Japanese movie theaters, and the ads specifically highlight fine amounts, maximum sentences, and ask viewers to report suspicious behavior of others (all delivered with cute mascots). In comparison, I don't notice anti-piracy campaigns that much in U.S. theaters these days, and the ones I remember seemed to reinforce the message that piracy is a crime more generally rather than focusing on specifics of potential punishments, e.g. "You wouldn't steal a car" ads.
ISPs also have a reputation of being very cooperative with Japanese authorities, and since violations are serious criminal offenses, I get the feeling from friends that they consider it is a very serious risk. This is from my quite limited experience though, so I would be very curious to see stats on arrests, convictions, and sentencing. The wiki page you linked is definitely missing a lot of information.
(IANAL) In Japan, Streaming(watching) paid content is explicitly specified as legal meanwhile downloading is illegal. (Technically not different but this is law).
Yes public messaging on theater/TV is really annoying.
> ISPs also have a reputation of being very cooperative with Japanese authorities
I don't know. They mush provide personal info for IP address if they orderd from police with writ, but I don't know other case to coop to arresting (like censoring).
AFAIK, currently no one is arrested by just downloading a content (even illegal), but who use P2P that also uploading is arrested well.