Japanese fighter makes love (4)
I believe the answer is:
zero
This clue is a double definition.
'japanese fighter' is the first definition.
(I've seen this before)
'love' is the second definition.
(love is zero in tennis)
'makes' acts as a link.
(Other definitions for zero that I've seen before include "A very low temperature" , "Duck" , "someone extremely unimportant" , "Rock bottom" , "Naught" .)