Assassin from town in Japan (5)
I believe the answer is:
ninja
'assassin' is the definition.
(I've seen this before)
'from town in japan' is the wordplay.
'from' says the answer is hidden in the clue.
'NINJA' can be found hidden inside 'town in japan'.
(Other definitions for ninja that I've seen before include "Mercenary in feudal Japan" , "martial art expert" , "14th-century Japanese soldier of fortune" , "Ninjutsu expert" , "Japanese stealth fighter" .)