Consciousness of Arill
While the Arill were considered an obvious physical threat, their methods of existing meant that they still posed a significant danger to Earth when they came to the planet.
They are a race of pure consciousness, the Arill required networks to survive, existing in connections of power, trolling through non-physical areas such as cyberspace and drawing on electrical power to sustain themselves. Typically they parasitized energy sources without causing too much trouble, arriving on planets operating on a war footing where governments would have large enough budgets to compensate for the power drains they caused, but this worked against them when they arrived on Earth in the age of the Vikings, at a point when no such electronic system existed.
With no power supply to draw on to sustain themselves, the Arill tried to possess and harness the electrical energy of the human brain, but the brains naturally lacked the energy to sustain the Arill for long. Unable to exist in Earth’s natural atmosphere without bursting into flames, the Arill concealed themselves underwater, manifesting from the ocean in the form of fire as they tried to acquire new power sources. Their attempts to ‘possess’ humans and ‘link’ them together in the same manner as the Arill were connected inevitably resulted in their hosts being destroyed as they were unable to cope with the energy being channelled through them, with the fires destroying any Viking ships that were unlucky enough to encounter them.
Shortly after the Arill had arrived on Earth, the Vikings that were being plagued by the Arill were fortunate enough to encounter the Eleventh Doctor, currently travelling alone and looking for a chance to play a game on the famous Lewis chess set, The Doctor helping to save a Viking ship and convince a nearby village to offer the Vikings somewhere to stay. When another Viking ship was narrowly saved from the same flames, The Doctor learned that one of the crew had been possessed by the same entity, but was only able to learn that it sought to continue ‘the line’ before its host was incinerated. When the new ship departed again, attempting to take Princess Freydis to her arranged marriage, The Doctor had also tried to follow in the TARDIS, but although he was able to materialise on the ship and rescue Freydis, the TARDIS was so heavy that it sank through the ship, and the presence of the Arill caused the TARDIS to shut down all but the basic essentials of its own power in order to prevent them accessing its systems, resulting in it sinking rather than dematerialising.
Using a diving suit in the TARDIS’s storage bays, The Doctor left the ship to try and communicate with them, but they were unable to understand his efforts to explain why this world wouldn’t be able to support them, although he was able to distract long enough to get the TARDIS back to the surface. With fires forbidden in the village to limit the Arill’s opportunity to travel, The Doctor attempted to send them a message to leave via the psychic paper, but they merely used this opportunity to trick him, appearing to disperse into the sky and subsequently using a small torch to ‘infect’ a passing Viking who attempted to pick it up after spending the previous weeks dealing with the cold.
With the Arill having exhausted The Doctor’s willingness to find another way, he decided to use the sonic screwdriver and a metal rod to assemble a makeshift lightning conductor, subsequently going out to sea in a coracle during a storm and dipping himself into the water so that he could communicate with the Arill. Offering himself as a host – his Time Lord physiology capable of channelling far more energy than a human, The Doctor absorbed the Arill completely into himself before using the storm and his makeshift conductor to attract a lightning-bolt to his coracle, the resulting energy discharge providing the Arill with a new path as they followed the lightning up into the sky before being dispersed across the upper atmosphere, becoming the Aurora Borealis.