Requires brushes stored inside case when finishing these, on reflection (5)
I believe the answer is:
needs
'requires' is the definition.
('need' can be a synonym of 'require')
'brushes stored inside case when finishing these on reflection' is the wordplay.
'finishing' suggests the final letters (the letter which finishes the word).
'these on reflection' shows that the letters should be reversed in order.
The final letters of 'brushes stored inside case when' are 'sdeen'.
'sdeen' in reverse letter order is 'NEEDS'.
(Other definitions for needs that I've seen before include "Calls for" , "Necessitates" , "shopping-list, say" , "Essentials" , "Necessities" .)