Kiruru is a character from the anime movie Keroro Gunso the Super Movie. Also he was in Keroro Gunso when he was a tadpole.
Kiruru initially appears as a serious silent Keronian, floating in the night. Although he has been shown to emit sounds, he never engaged in conversation with anyone. He is said to be the Keron Army's greatest weapon of destruction.
Kiruru's initial form looks almost like a standard adult Keronian. He has white skin, with the usually white areas under his mouth and on his belly colored dark gray or black. He has slanted blue eyes and there's no visible division between his hat with the ear covers and his actual head. He has a green X mark on his forehead and a red one on his belly, and he also wears a yellow bracelet on his right wrist.
In his second form, he becomes a giant. His body stretches out, with his head becoming proportionally smaller, and there is a visible division between his helmet, which replaces the flaps with two blade-like structures. The symbol on his head becomes red and distorted, with the superior part of the X becoming much larger. There's also a second X mark on his back. He acquires a long forked tail, colored mostly gray, only the edges being white. His arms also are proportionally larger and are almost touching the ground. The bracelet disappears, but yellow patterns similar to it are visible on his arms.
In his final form, he becomes a large gray tower, built by plates that also spread themselves all around it destroying anything built nearby. Kiruru's large red X mark in this form is actually a barrier blocking access to the core of the tower, where there's a large orange crystal.
In his first form, Kiruru is able to spread "X" marks to his targets around the world. These "X" marks give the targets the ability to read minds of other people with similar marks, and the one who receives the mark can also transmit it again. After a while, the marks start spontaneously receiving negative thoughts from nearby bearers, trying to put down the user. These negative feelings, pain, worries, conflict, are transmitted back to Kiruru, giving more energy to him.
For direct combat, in this initial form, he's only shown to have the ability of free flight, in speeds comparable to Keronian vehicles.
After absorbing enough energy, Kiruru takes a giant combat form. In this form, he's able to take high amounts of damage, from missiles to energy attacks, without even flinching. He hasn't been shown to use his flight ability in this form though, but he's still able to absorb energy from negative emotions.
In his final form, Kiruru becomes a tower that continuously spreads plates around the planet's surface. The central tower quickly creates a high number of Kirurus identical to the first stage described above, although they're still connected to the central unit, and disappear after it's defeated. Mirara says that this last stage is able to destroy a planet. In volume 13 of the manga, a similar Kiruru in this final stage destroyed the planet Altea 7, reducing it to a giant rock.
Kiruru is an artificial Keronian, part of the "Self Decision Making Ultimate Invasion Weapon: KiruMira". The one to carry through the invasion was Kiruru. The decision maker: Mirara. In ancient ages, he was created by the Keronian army and used on Earth, destroying the dinosaurs. However, it was sealed afterwards.
In the extra manga chapter from volume 13, it's revealed that the ancient Kiruru was motive of shame for the Keronians and the space police even questions Keron's military when a small sign of Kiruru's activity is found. His existence is a secret erased from Keron's history books. Even when the Garuru platoon receives a mission to destroy the unit that attacked and destroyed Altea 7, only Garuru himself receives an official mission briefing about Kiruru. With the "type three special weapon handling device: KiruMira Deleter", Garuru destroys the Kiruru with a single shot. However, another Kiruru unit still existed elsewhere.
On Earth, an ancient Kiruru is awakened when Keroro and Fuyuki find an ancient shrine hidden by a strange anti-barrier, breaking a small crystal there. Keroro tries to put it together again, but it didn't stop Kiruru.
Quickly, Kiruru spread the X marks throughout the planet. The people who received the X mark, seemingly gaining telepathic powers became known as Revolutors, while the new telepathic communications was called "Revolutor Communication" or "Revocommi", considered to be a method of communication that surpassed cells and internet. However, human civilization quickly fell apart when each person started noticing the negative thoughts of others. Kiruru silently absorbed that negative energy, eventually transforming to his second form. In his giant form, Kiruru started to walk though Oku Tokyo, damaging everything in his path. The Keroro platoon's attempts to defeat him with physical strength turned out to be pointless and, after absorbing the energy of Keroro's fear and frustration, he went to his final form.
Keroro and Fuyuki, learning Mirara's real identity as a component of Kiruru, and chosen by her to stop him, flew to the tower. Kiruru started multiplying itself, creating an army of first stage Kirurus, but, with help from their friends, Keroro and Fuyuki entered in the tower, carrying Mirara in key form up to the core, which resembled a giant version of the crystal initially broken. Arriving there, they inserted the key, sealing Kiruru and Mirara again. The tower vanished alongside every Kiruru copy, leaving no visible traces of its existence behind. A few years ago on Keron authorities were looking for an escaped bio-tech weapon that actually was a Kiruru possibly because keronian scientist were working on a new version of Kiruru, but it had escaped.
Kiruru's name comes from the English word "Kill", written in Japanese as Kiru (キル).