The insect's final appearance is based on the carrier's true nature, and is very likely to inherit similar features.
A Loyal Minion
After the Kokuboro declares war on the Kekkaishi of Karasumori, Kaguro visits Gen and offers him the chance of joining Kokuboro. He then gives Gen an Ayakashi insect egg, which he says will never betray him. The egg was given to Kaguro by Byaku in hopes of somehow turning Gen against the Kekkaishi. Byaku explains that when the egg hatches, Gen will become one of them and obey every command of Byaku's. Gen becomes conflicted by the egg's advice, as it constantly points out that he is different and that normal people consider him a monster, but that part of him would be acceptable in Kokuboro. However, after learning that the Kekkaishi also accept him in his full Ayakashi form, Gen's mind becomes clear, and after the insect emerges from its egg, he crushes it.
Powers & Abilities
Host Manipulation: Once attached to a host, an insect can easily manipulate the host's mind, tricking them into believing that they are an outcast, and gradually separating them from human contact.
Host Mimicry: While in egg form, an insect gradually develops into a shape similar to the current owner of the egg, which is revealed upon hatching. Supposedly, the insect will remain loyal to the owner, but most likely their actual loyalty is to whoever controls the insect that initially laid the egg.