The Spirit of the Body is the ghost of one of the Bach Brothers and one of the guardians of Silverlight. During Demon Slayer, ten of its skeletons must be slain before it will allow you to retrieve the sword.
He also makes an appearance in Dimension of Disaster: Demon Slayer. Players must exorcise him from the zombified Dr Harlow using a sobriety potion in a beer glass. After being removed from Dr Harlow, the spirit will still demand a trial and ask for the player to kill anything in the bar; alternatively, the player can have him kill them (players will not lose items dying this way). Either method will satisfy the spirit and he will lift his part of the barrier for players to collect Silverlight.