A person that really suits eimi, taking a stimulant drug (7)
I believe the answer is:
someone
'a person that really suits eimi taking a stimulant drug' is the definition.
'someone' can be an answer for 'a person' ('someone' can be a synonym of 'person'). I'm not sure about the rest of the definition.
'a person that really suits eimi' is the wordplay.
I cannot really see how this works, but
'a' could be 'one' and 'one' is found within the answer.
'really' could be 'so' (both can mean 'extremely') and 'so' is found in the answer.
'eimi' could be 'me' (where the crossword setter is 'Eimi') and 'me' is found within the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for someone that I've seen before include "Unspecified human being" , "individual" , "Unspecified person" , "Important person" , "big cheese" .)