For Americans, it's worth noting that Japanese apartments don't come with appliances. You'll get to buy your own fridge, microwave, and washing machine. Dishwashers are insanely expensive, and some older places don't even come with a stove.
Appliance sales here are like car sales in the US, so negotiate the bejeezus out of them. A friend of mine picked up a free 50+ inch brand-name TV when he bought his refrigerator and bistro oven, to give you an idea of what's possible.
This is an important point especially if just wanting to stay short-term. Furnished places for rent are extremely rare. Pretty much the only chance for that is if you go through an agency which targets foreigners and you will pay through the nose for that.
Sometimes though appliances are included. My flat included a small bar fridge. Another flat I looked at (but didn't rent) included a washing machine and TV.
You'll also need your own washing machine. Rental buildings don't have a common laundry room.
Appliance sales here are like car sales in the US, so negotiate the bejeezus out of them. A friend of mine picked up a free 50+ inch brand-name TV when he bought his refrigerator and bistro oven, to give you an idea of what's possible.