mains electricity in Japan: split-phase?

In the US, we use a split-phase power system: two wires (call 'em A and B) each carry AC voltage a half-cycle out of phase with each other, and a third wire functions as ground. Need 110 volts? Attach your appliance to wires A and ground, or to wires B and ground. Need 220 volts? Attach your appliance to wires A and B.

Is Japan’s electrical system for residential buildings set up this way? Or can you only get 100 volts in a house?

As a furriner, I don’t believe your usage of phase is correct, or at least we do not use that word to describe what you are using.

We would call it a centre tap system.

Same thing; see my Wikipedia link.

At least some houses in Japan have special sockets with 200V (live-to-live) for cookers and air conditioners. I don’t know how widespread this is.