Keen on (4)
'keen on' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for into that I've seen before include "Four this twelve is three" , "Teachers' trade union" , "Keen on, colloquially" , "A fan of" , "Showing enthusiasm for" .)
(Other definitions for fond that I've seen before include "Affectionate - tender" , "Partial to" , "Feeling affection, maybe foolish" , "Affectionate, maybe foolish" , "Keen on; indulgent" .)