Tanaka is an amnesiac woman who Illya first encounters upon her arrival in Miyu's World. She has no clue about her past and the only thing that she remembers is that she must defeat the Ainsworth as they have nefarious intentions in her words. It is later revealed that she is a manifestation and the last survival instinct of the dying Gaia, Earth's counter force and the opposite of Alaya, Humanity's counter force, serving as its Counter Guardian in the face of the overwhelming threat of the "corrosion of the world on the other side of the hole".
Tanaka is an amnesiac woman who tends to forget a lot of things except for her name. However she is upbeat, cheerful, she is also considered the comic relief when she's not serious. She tends to sleep when she doesn't understand what people are trying to explain.
Tanaka has the mind of a child, which was stated by Illya. For some reason, Tanaka likes to wear gym clothes instead of wearing regular clothes and doesn't like Erika Ainsworth. However, during crucial moments, she will go into a trance and perform feats that cannot be classified as human such as regenerating.
While she entrusts the fate of the planet to Illya, as a terminal for Gaia, Tanaka is ultimately indifferent to the survival of humanity itself.
Fate/kaleid liner PRISMA☆ILLYA
While Tanaka has shown no extraordinary skills, likely due to her amnesia, she does possess several passive abilities in regards to her body that are superhuman in nature which render her indestructible.
Tanaka is immune to any changes in temperature, whether hot or cold. During her encounter with Darius Ainsworth, she starts to generate enough heat to burn Kuro on touch. This effect seems to be continuous as even after the battle, she continued to generate enough heat to make the room she was in uncomfortably warm.
She has also shown to be immune to any kind of damage. Repeated attacks by Beatrice, while equipped with her Berserker Class Card including taking a direct hit from its lightning strike, that Beatrice stated would vaporied anything, failed to do any damage, instead simply destroying her clothes.
During the initial encounter with Darius Ainsworth, Tanaka entered a trance-like state where, using an unknown ability, she managed to create a blast which destroyed the Noble Phantasm Apneic Beauty where even a direct hit with Caladbolg II from the Archer Card had no effect.
Her arm can be detached and become a sword that is able to cut through the mud cube. Erika recognizes it as the World's "truth" that passes judgement on the counterfeits. It is also shown to be too hot to wield, causing Kaleido Ruby to wrap around it in order for it to be wielded by Illya.