Well, I love anime and great music ^^

What an odd mix of oh-so-cute manga stuff and great music-tracks, haha.

breakcore is composed mostly of breaks (samples from songs). these breaks are generally drum samples of sorts, at least in this genre. This method is also used in alot of rap, but to a much lesser degree. Rap is usually a four count drum loop, whereas breakcore can take any count or measurement. IDM, is traditionally made up entirely by the composer, that is, although samples may be used within IDM, the prominance of the sample isn't as abundantly clear as in breakcore. One could argue that IDM typically has a better production level than breakcore, but this can only be supported by artists that are distinguished by one of the two genres. Also, the genres are diffferent because of the scenes that come with them; that's typically how genres are even formed.
so there you are, my comparison of breakcore and idm.

Wow, I really have to agree with your comment on the Gunnera video. Cathart and Gunnera are, like, my favorite songs ever but am not overly astounded by most of their other songs. However, you should give the album Meet Next Life (which is the one with Gunnera on it) a try. It's all really good stuff, and much more all-around enjoyable than Plans Drawn in Pencil or Lucky Cat, in my opinion.