The Embedded was once a human who realized that he could never resist the temptation of the flesh, so bound himself eternally with chains at the top of the tallest tower in Drangleic Castle. Since then he has awaited the day that somebody will find the Key to the Embedded, found on the body of the Demon of Song and plunge it into his face, thereby bringing a rhapsodic end to his fate.
The Embedded was perhaps a member of the clergy involved with the Shrine of Amana. He was presumably a contemporary of Vendrick, as he is chained up in Vendrick’s castle which we know was built by golems after the invasion of the land of the giants. The Embedded clearly struggled with temptation, but what he was tempted to do is questionable. It seems he faced various temptations. Being subject to the temptation of the flesh is a phrase associated with lust, but can apply to any of the vices. The Ring of the Embedded implies that the Embedded was a slave to all forms of pleasure. It is even implied that the Embedded is a masochist, as killing him is described as bringing “a rhapsodic end to his fate”.
The Embedded and the Demon of Song are clearly linked in some way. The Demon of Song’s soul description says that it developed a taste for human flesh, while the Key to the Embedded says that the Embedded realized that he could never resist the temptation of the flesh. When the Embedded realized he couldn’t resist, he bound himself in chains and when it was realized the Demon of Song had a taste for human flesh, it was contained in the shrine. Furthermore, The Embedded bares all for anyone to see, hiding only his face behind the mask, the Demon of Song hides within the body of a toad, and is only a face, arms and hands. The putrid and pallid skin colour of both the Demon of Song and The Embedded is also coincidental. The Demon of Song has captured the voice of a Milfanito which wastes away in a hut just outside its lair, and The Embedded is the gatekeeper to a cage that houses a healthy Milfanito. These may simply be dismissed as coincidences, but their relationship is cemented by the fact that the Demon of Song drops the Key to the Embedded when defeated.
In a cage behind The Embedded is a trapped Milfanito. The only entry into this cage is by killing The Embedded with the Key to the Embedded. How this Milfanito came to be in the cage is unclear. When you speak with it, it exclaims and then disappears, then while travelling down the elevator of the tower you hear its song. The other Milfanito commend you because you “rescued a Milfanito who was taken from us”. The guidebook also mentions when talking about Milfanito that some have been taken by those with ill intentions. It would seem then that The Embedded kidnapped a Milfanito, perhaps because of lust. It may be that The Embedded kidnapped the Milfanito and it was at that point he realized he had gone too far… Or perhaps The Embedded did this so that someone would have incentive to find the key and kill him, thereby saving the Milfanito trapped in the tower.
How The Embedded and the Demon of Song are connected is unclear. Like the Covetous Demon, it could be that the Demon of Song was overcome by a powerful emotion and transformed, hiding in a toad perhaps as a subconscious manifestation of shame. It may be that The Embedded we find in Drangleic Castle tower is the true body of the Demon of Song, and the Demon itself is just the face of The Embedded.