Infant

The Infant (赤子, Akago) is Naraku's heart and seventh detachment. Despite his appearance, he is capable of speaking fluently. His main power is to control people with the darkness in their own hearts. He attempts to control Kagome's mind by finding pain or anger within her heart, and use her abilities to find the remaining shards of the Shikon Jewel. He finds her jealousy of InuYasha's feelings for Kikyo, but InuYasha saves her before The Infant can control her. For this same purpose - to find the Shikon Jewel -, he's taken by Kagura to temples inhabited by powerful priests. The plan was to kill the priests and read the their souls as they departed from this world (Naraku had suspicions that the Shikon Jewel had been taken to the world of the dead). In one such confrontation with a priest, Akago is broken into two. Both halves survived. One grew up into Hakudōshi; the other, which contained Naraku's heart, remained in a baby form. For that reason The Infant was deemed as more important than Hakudōshi, who himself was empty just like Naraku. Like Kagura, The Infant is not loyal to Naraku, and he and his other half eventually betray him. However this backfires and he is absorbed along with Moryomaru by Naraku.

Abilities
Manipulation: Akago had the ability to search deep within a person's heart for darkness and if they didn't have enough willpower to resist him, they would be under his control.

Barrier Erecting: Akago was able to erect strong barriers (like his master, Naraku) to defend himself. However, when he revolted against Naraku, the ability to do this was disabled.

Trivia
English-speaking fans often think of Akago as the 'real name' of the character the dub only calls "The Infant." However, akago merely means 'baby.' In both versions, his only name is that simple descriptor.