In Japan I mustn't find hostility (6)
I believe the answer is:
animus
'hostility' is the definition.
(animus is a kind of hostility)
'in japan i mustn't' is the wordplay.
'in' indicates the answer is hidden within the clue.
'ANIMUS' is hidden in the letters of 'japan i mustnt'.
'find' is the link.
(Other definitions for animus that I've seen before include "Motivating spirit" , "Malicious ill-will" , "US man I turn to with hostility" , "Hostile feeling" , "Hostile spirit in speech or action" .)