Ultimately alive and kicking, very irritable (4)
I believe the answer is:
edgy
'irritable' is the definition.
(thesaurus)
'ultimately alive and kicking very' is the wordplay.
'ultimately' suggests the final letters.
The final letters of 'alive and kicking very' are 'EDGY'.
(Other definitions for edgy that I've seen before include "Anxious" , "Uneasy" , "Overstrung" , "Visibly nervous" , "Red shade" .)