Im not trying to say its in either the dark keyblade or kk but im saying that maybe Ven went to Riku with Terra's keyblade not in it but with it and when sora reached into riku and stole his keyblade ven's heart followed so as to stay safe with the kk and stronger heart but when sora used the dk on himself along with releasing his and kairi's ven's went to and stayed with sora's body and soul making roxas look like him and have emotions
Since the heart wasnt his i think technically roxas was still a nobody but because a heart was so close to being his it made him have emotions and take ven's form
Since the heart wasnt his i think technically roxas was still a nobody but because a heart was so close to being his it made him have emotions and take ven's form