Dating
Alright, maybe not entirely necessary...but if you feel embarrassed to ask others for resources or just want some inside advice, check out the rest of this page.
Pairs
The interface is entirely in Japanese, so if you don't speak Japanese you'll definitely want help setting it up. This app is more geared towards serious relationships. But be warned, it's for heterosexual relationships only.
Tinder
Yes, that Tinder. It exists in every country. One thing to be warned of is that many girls seeking girls are looking for platonic friendships. Many dating apps in Japan are not geared toward same-sex relationships.
Join a Club
You read that correctly. One great way of meeting people is by joining a club (sports, tea ceremony, dance, whatever floats your boat). Meeting people through these activities guarantees at least one thing in common, and makes it easier to make a more natural connection.
Contains multiple blogs regarding dating in Japan. And yes, those are penguins. Deal with it.
Facebook Groups
There are also some Facebook Groups for dating in Japan. I've only ever known of groups geared towards Ladies/Women//Females, so I'm sorry guys. If you are curious of these groups and you fit the above description, check out JET Ladies+ or Futon Party. These groups won't feel like safe spaces for everyone, so keep that in mind and participate at your own risk.