Takeshi Kovacs is the Sky Dweller Takavatch, who chats to Ringil occasionally. Takavatch states that he could 'flit between the stars as a song' (needlecasting), could call upon the fire of the gods (angelfire, from the Martian weapon platforms) and was a member of a group called the Ahn-Foi (Envoys).
There are also references to sleeving and to Quell as well.
What is dividing fans is whether the planet in The Steel Remains and Cold Commands is Harlan's World or Earth. The latter seems most likely, as much is made of the planet having a former satellite called Muhn (Moon) which was destroyed to form the planet's ring system.