Hero decides to show how to eat away (5)
I believe the answer is:
erode
'to eat away' is the definition.
(synonyms)
'hero decides to show' is the wordplay.
'to show' indicates the answer is hidden within the clue.
'ERODE' is hidden within 'hero decides'.
'how' acts as a link.
(Other definitions for erode that I've seen before include "Wear away with weather" , "Corrode" , "Become ground down or deteriorate" , "go to pieces!" , "Grind down" .)