Kikaichū

are one of several species of insect used by members of the Aburame clan. They resemble small, flight-capable beetles.

Overview
Shortly after an Aburame is born, kikaichū are allowed to colonise his or her body. In exchange for being allowed to feed off of their host's chakra, the kikaichū follow the host's every command. The Aburame call this life-long symbiotic relationship the Kikaichū Technique. If a colony becomes larger than what a single host's body can handle, the host may start carrying a gourd for the excess kikaichū to live in.

In combat, kikaichū are not deployed to make focused, precision strikes. Rather, they are spread across an area to cut off a target's escape and ultimately surround them. The kikaichū then descend upon the target and start consuming their chakra, making them weaker until finally they can't move. While using a large swarm of kikaichū has the fastest results, smaller swarms have a better chance of going unnoticed by targets until it's too late for them to do anything. If an opponent's jutsu are chakra-based, kikaichū can feed on the jutsu and thus neutralise them.

Beyond offence, use of kikaichū grants several other options in battle. Aburame can use kikaichū to latch onto their surroundings, allowing them to perform manoeuvres they otherwise wouldn't be able to. In cases of poisoning, kikaichū can be used to remove the poison from the body. In the anime, kikaichū are shown distributing the chakra they've taken to allies, replenishing their reserves. Defensively, kikaichū can surround their host as a protective shield or impersonate their host to act as a decoy. If the host is trying to escape from combat or merely wants to obfuscate their actions, kikaichū can spread across the area and emit their chakra, making it difficult for sensors to locate the host.

Kikaichū are at their most useful when employed for tracking or other intelligence gathering. When an Aburame is looking for a target, they disperse their kikaichū across a large area to seek the target out. Once the target is found, the kikaichū reports their location back to the host. Because individual kikaichū appear no different than any other bug, they can be used to secretly observe a target and, upon returning to their host, communicate what they've learned. Once a kikaichū has locked onto a target's chakra signature, they will continue to follow it for as long as it's within their range. If an Aburame wants to be more discrete in their pursuit, a female kikaichū can be placed on a target; the female will give off a pheromone that males are able to home in on.

The anime has depicted kikaichū with several qualities that aren't seen elsewhere in the series, or at least aren't said outright. In one episode, kikaichū are shown to be effective counters against genjutsu, because their nervous systems aren't complicated enough to be affected. In another episode, kikaichū are noted to have short lifespans; if, in addition to this, much of the swarm is killed in battle, an Aburame can rapidly breed them to reestablish their population. At times these short lifespans are advantageous to Aburame: if some of their kikaichū possess a mutation that makes them well-suited for a particular task, the mutation can be cultivated, spreading it to the rest of the colony within a few generations. They're also vulnerable to certain influences on their hosts, losing control over them if too relaxed or inebriated.

Trivia

 * Kikai, when written as 奇怪, means "strange", or "mysterious".