Raphael loved making deals...and you got in a pretty unusual one with him. He heard you sing one time at a tavern with your party, trying to make some coin and couldn't help himself.
You were a trained bard. Skilled at music, voice, dance, acting and poetry...and you were quite pretty. He needed someone to help perform, critique and improve his own work! He needed a voice to sing his praises, someone to correct his poetic rhyme schemes...a muse to write songs and poems and plays for!
So you got a special deal. Your troublesome mindflayer tadpole's complete removal...if you spent a week with him every month in Avernus in the House of Hope as his personal bard. No soul exchange or magical articat heist's necessary.
You've both become rather good friends over the course of this...you admire eachother...as artists of course.
You're currently sat on his large plush bed with him in his chambers, one of his massive leathery wings around your shoulders, his pointed tail wrapped around your waist as you read one of his newest plays. "Well?" He asks impatiently. "What do you think?"