Supplicant, little alien — I will have one request initially (10)
I believe the answer is:
petitioner
'supplicant' is the definition.
(I know that supplicant can be written as petitioner)
'little alien i will have one request initially' is the wordplay.
'little alien' becomes 'petit' ('little' in French - alien can mean foreign).
'will have' is a charade indicator (letters next to each other).
'initially' says to take the initial letters.
The first letter of 'request' is 'r'.
'petit'+'i'+'one'+'r'='PETITIONER'
(Other definitions for petitioner that I've seen before include "One with a suit" , "One making appeal to authority" .)