Character’s new, not initially fully developed (6)
I believe the answer is:
nature
'character's' is the definition.
(I've seen this before)
'new not initially fully developed' is the wordplay.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'not initially' means to remove the first letter.
'fully developed' becomes 'mature' (I've seen this before).
'mature' with its initial letter taken away is 'ature'.
'n'+'ature'='NATURE'
(Other definitions for nature that I've seen before include "sort of reserve" , "Power underlying the world" , "Basic character" , "Character - our Mother" , "scientific journal" .)