If you're here and able... Learn a martial art.
This sport is only recommended for those
who want to do this and have the time.
I've known a number of foreigners who've been here for a short time and who've become members of Toyano Taikukan (Gym). Toyano Gym has a number of martial arts programs including Judo, Aikido, and Japanese archery.
You'll need to check with the Gym's staff for time schedules. Of course if you join one of these sports, you'll need the equipment. For example, if you're going to do Judo, you'll need a Judo gi (robe). You can buy one and other martial arts materials at a martial arts shop located across from Hakusan Park.