Unaware first pair of lions occupies plain (9)
I believe the answer is:
oblivious
'unaware' is the definition.
(similar in meaning)
I don't understand the rest of the clue.
(Other definitions for oblivious that I've seen before include "Totally unaware" , "Blind (to)" , "Unconscious" , "Absent-mindedly unaware" , "In ignorance" .)