I used to have a TV in my apt's room (LeoPalace) and used to watch Japanese TV but I replaced it with an iMac and thought I could just watch Japanese TV online or something when I needed it. Well, no, Japanese TV is in HD and often shows display (or can be set to display) subtitles in Japanese. I don't want to bring back the TV though. Can I use the iMac as a TV?

You need a digital TV tuner. I googled "imac テレビ" and these are from the very first hit:

http://www.pixela.co.jp/products/tv_capt...hi_vision/
http://www.pixela.co.jp/products/tv_capt...dt181_pu0/
http://www.iodata.jp/product/av/tidegi/gv-mactv/

[s0apgun]

I use an Elgato Eye TV 250 works great