Soon after relocating to Japan, you'll want to get some essentials like a dakimakura to keep you company, and maybe some wrist support so that you dont break your arm when working hard at your new job. After that you'll probably want some furniture and some other necessities around your apartment.
In our 13 years of living in Japan, we've never come across anything cheaper than Ikea - cheap and the quality is decent too. I hear many folks knock Ikea but its good enough for us and we've been happy with their stuff for many years now.