Black Judge:
Your brother's hunger for your sins is not yet sated. Your penance must continue... All the terrible feelings that you are experiencing... the feelings of embarrassment, confusion, loneliness, and boredom etc... they are the manifestation of your sins that are now getting dissolved and exposed...
(When the Sin Eater advances one level you will have completed this quest.)
All of the Exp that the character who summoned the Sin Eater has acquired will be transferred to the Sin Eater.
When the Sin Eater becomes hungry, you can feed him "Food For Wolves."