Japanese island hard on footwear we hear (6)
I believe the answer is:
honshu
'japanese island' is the definition.
(I've seen this before)
'hard on footwear we hear' is the wordplay.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'footwear' becomes 'shoe' (shoe is a kind of footwear).
'we hear' shows a homophone (sound like).
'shoe' sounds like 'shu'.
'h'+'on'+'shu'='HONSHU'
(Other definitions for honshu that I've seen before include "The largest island unit of Japan" , "Largest island of mainland Japan" , "Island regarded as the Japanese mainland" , "Largest of the four main islands of Japan" , "The main island of Japan" .)