Infant

The Infant (赤子, Akago) is Naraku's heart and seventh detachment, and is capable of speaking fluently. He is a baby that can control people with the darkness in their own hearts. His main goal is 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. Like Hakudōshi and Kagura, The Infant is not loyal to Naraku, eventually even betraying him. However this backfires and he is destroyed 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
Akago's name was never mentioned in the English version of the anime. Instead, he was just referred to as "The Infant". His name was never even mentioned in the credits.