I had to enter battle with this character! (6)
I believe the answer is:
friday
'this character' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'i had to enter battle' is the wordplay.
'i had' becomes 'i'd' (contraction).
'to enter' is an insertion indicator.
'battle' becomes 'fray' (fray is a kind of battle).
'id' put inside 'fray' is 'FRIDAY'.
'with' is the link.
Can you help me to learn more?
(Other definitions for friday that I've seen before include "'Robinson Crusoe' character" , "Muslim Sabbath" , "Crusoe's Man (Defoe)" , "Man perhaps" , ""Good" day at Easter?" .)