Northern character one sent off of course (5)
I believe the answer is:
natch
'of course' is the definition.
(short for 'naturally')
'northern character one sent' is the wordplay.
I cannot really understand how this works, but
'northern' could be 'n' (abbreviation e.g. N. Ireland) and 'n' is present in the answer.
'character' could be 't' and 't' is present in the answer.
'one' could be 'a' (a thing is one thing) and 'a' is found within the answer.
The remaining letters 'ch' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'off' is the link.
Can you help me to learn more?
(Other definitions for natch that I've seen before include "Of course! (US sl.)" , "a display of Indian dancing" , "obviously" , "Of course, commonly < , behind" .)