Remains precisely how he is (5)
I believe the answer is:
ashes
'remains precisely' is the definition.
'ashes' can be an answer for 'remains' (I've seen this in another clue). I'm not sure about the 'precisely' bit.
'how he is' is the wordplay.
'how' becomes 'as' (I can't explain this - if you can you should give a lot more credence to this answer).
'he is' becomes 'he's'.
'as'+'hes'='ASHES'
Can you help me to learn more?
(Other definitions for ashes that I've seen before include "Test-match trophy" , "Powders remaining after fire" , "Residue form fires" , "Test cricket series" , "Residue from fire" .)