Quote Originally Posted by Veloran View Post
The aetherial sea isn't the space between the Shards. If it was, souls would just rejoin in the sea as they naturally do after a rejoining. Basically it appears each Shard's Lifestreams are not connected to each other.
Each Lifestream is attached to the Aetherial Sea. This much is apparent due to Minfilia getting sucked into the Flow teleportation magic that spirits her through the Lifestream to the Aetherial Sea. And it is where Hydaelyn resides and keeps watch on all shards, so yes, it is.