The Infant (赤子 Akago?) is Naraku's heart and seventh detachment, appearing in the form of a human baby yet can speak fluently and control people with the darkness in their own hearts. It is later revealed that the Infant's appearance was intentional by Naraku as he expected the detachment to be as devious as himself. His goal was to use Kagome 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. Because the Infant possesses his heart, Naraku had the infant placed under much protection. But overtime, the Infant and Hakudoshi conspired to destroy Naraku while making themselves the dominant aspect of his being.
To that end, Hakudoshi provides the Infant with Moryomaru (魍魎丸 Mōryōmaru?), a 100-foot-long (30 m) demonic golem created from demons who was briefly sealed in the body of a monk named Goryomaru (御霊丸 Goryōmaru?) before assimilating the human's body after he was killed by Hakudoushi. While Moryomaru was originally a puppet, he gains a mind of his own when the Infant is placed inside of him. Acting as a medium of the Infant's will to become a dominant aspect of Naraku, Moryomaru goes to absorb different demons to increase his power to the point of nearly defeating most of Naraku's enemies when they ganged up on him as he destroyed Tokijin before running off. However, Moryomaru meets his end when tricked into absorbing Naraku, enabling him to reabsorb the Infant and consume Moryomaru from the inside out.