I don't mean to be dismissive, BUT...
You want to become a police officer in Japan for some unexplained reason, yet you are so ridiculously far from achieving ANY of the minimum requirements for the job.
Are you a Japan national? No
Did you go through The Japanese education system? No
Do you even speak, read or write Japanese? No
Do you meet any of the minimum requirements for even getting a visa to live in Japan, let alone citizenship?! No
The people above are being a little too kind, perhaps out of fear of being admonished. At this point, you might as well be planning for your next life. There's no guarantee that even after all the years spent just trying to make yourself eligible you'd even be accepted into the academy, or pass through the program, or get an appointment, or even like your job when you get stuffed into a tiny koban in tottori.
Go and visit and enjoy yourself. You'll probably see a lot of Japanese police as they stop you and harrass you for looking suspicious. Study Japanese if you want, that's at least a reasonable goal. It helps when your goals have a solid foundation in reality. You've never been to Japan, yet want to denounce your citizenship to work and live there? Whose koolaid have you been drinking?