Semyaza is the leader of the fallen angels. He was also an Elder of the Council. He was greviously wounded during The Fall and had to be confined in a life support system.
Chapter 02: The TowerEdit
As Enoch is about to enter The Tower, all seven Grigori - including Semyaza - appear before him. This is likely an illusion cast by Sariel immediately after his first fight with Enoch.
Of the seven, only four have anything to say to Enoch. Semyaza is not one of them.
Chapter 11: Semyaza's DreamEdit
Once Enoch reaches Semyaza's floor, which is at the top of The Tower, Azazel reveals the pain of the Fall is beyond one's imagination. He also reveals that several of their number did not survive it.
When Enoch and Ishtar unlocks his confinement, Lucifel reports to God that there is no trace of Semyaza from inside the device and says that Semyaza has been dead for a long time.
- The manga presents Semyaza as lusting after a particular long-haired woman. He wished to meet her before his Fall but given what happened to him, they likely never met.