What book mentioned the seven demons? What plans has anyone made for them?

Radicals Handbook, pg97

Currently harassing PC's with the cleaning up of the residual effects of the tyrant star and they're not near any of the domains of the 7, so not a lot of use for them at present to be expanded upon.

After finishing the Haarlock trilogy, see my posts in GMs section, I think the Seven Demon thing is actually now going to be the main focus for my players at Ascension level. The Haarlock trilogy was a just a prelude to the real big stuff and that Haarlock was just a detailed story about one of the Demons. The seven now need to do 'something' or 'something' to happen so that the Tyrant Star can be born properly.

Still a lot of work to do on this, so welcome any ideas people have concerning the seven.

The 7 are mentioned a lot in my Haarlock Legacy überthread in the Gamesmasters section. Check out the recent reply by Bladehate who offers a nice suggestion how to tie all these mysteries together: Haarlock, Komus, the Hyades Locks, the 7 Devils.