For whatever reason I can't play it. I get some messages, but I dunno japanese and can't get it.

When using Replay Media Catcher you should start it first, start recording with it and only then open your web-browser and navigate to a web-page with embedded flash player and play the flash video.

You may also try to find the stream URL with freeware URL Snooper. It seems to be an RTMP flash video so you should add "flv;rtmp" to the "Also search for" editbox. After finding RTMP URL you may try freeware Orbit Downloader to downoad from it.