REI:“You hate being alone, don't you?
There are so many of us, and yet, you hate being alone.”
dzzthink: Only Rei would know that "there are many of us". She is essentially having a conversation with an Angel that knows her deepest darkest secrets and is being mocked for them.
UrsusArctos: This could be foreshadowing of the Reiquarium, but "there are many of us" could refer to human beings(Lilin) and suggest that Rei identifies herself as Lilin, not knowing the deepest, darkest secret about herself.