Such a forced wedding heartless for Japanese ruler (6)
I believe the answer is:
shogun
'japanese ruler' is the definition.
(I've seen this in another clue)
'such a forced wedding heartless' is the wordplay.
'such a forced' becomes 'shog' (I can't explain this - if you can you should give a lot more credence to this answer).
'wedding' becomes 'union' (I've seen this in another clue).
'heartless' suggests removing the centre.
'union' with its centre removed is 'un'.
'shog'+'un'='SHOGUN'
'for' is the link.
Can you help me to learn more?
(Other definitions for shogun that I've seen before include "Old Japanese hereditary army commander" , "No gush from this Japanese army commander" , "Dominant Japanese" , "Hereditary commander-in-chief in feudal Japan" , "Heredity commander of Japanese army" .)