The Japanese government doesn't give citizens private info to anyone other than the person themselves, a direct relative with good reason or a lawyer. You turn up at the city office, stamp your inkan and get a physical piece of paper with you and your direct families details on it.
Looking for any online/publicly posted records or applying for them is a dead end.
He would have had to register as a resident of Arakawa, but I strongly doubt he had citizenship. Much more likely to be a work visa. Maybe try to find out the company he was working at and see if that leads to any clues either way.