Assassin (Fate/Axiom ~ Yin & Yang)

Assassin (アサシン, Asashin) is a affiliated with Chāoguò, one of the main antagonistic groups within Fate/Axiom, holding the position as Black Tortoise of the Four Symbols. Assassin made their debut during the Metropolis Arc, where they were sent on a mission to inform about the Beifang, as well as providing Chaldea with a Flaming Shard.

Identity
Assassin's True Names are, a dualism concept found within Chinese philosophy. Yin cannot exist without Yang, and Yang cannot exist without Yin, forcing them to constantly exist, regardless if one were to be neutralized. When both Yin and Yang are able to put aside their differences, harmony is achieved.

Personality
Because of their very concept, Yin and Yang are almost constantly at odds with one-another, creating an unhealthy relationship between the two, where Yang is the dominant figure between them.

Following her characterizations, Yin is the timid, passive and reluctant aspect of Assassin. She does not seem to do well with others, even if it's just one person, often trying to hide away from the present conversation if at all possible. She also seems to not follow orders too well, almost always trying to go against them, if it means that she doesn't have to interact with anything. Yin is constantly being ridiculed by Yang, to the point that Yin would become afraid of him and bending to his will, just so he could leave her alone. Despite this, however, she cares for Yang and would often become more confident if he is in danger.

In contrast with Yin, Yang is the very abrasive, impatient and go-getter aspect of Assassin. He has no regard for the personal feelings of others, unless it's either Yin or Qin Shi Huang's, especially when it comes to the well-being of missions. Despite his impatience, because he was ordered to do so, he did not attempt to attack Chaldea during his visit, providing Chaldea with the information he was ordered to provide. Because of his intense demeanor, he is often manipulative to get what he wants, especially towards Yin.

Regardless of how dysfunctional their relationship can be at times, Yin and Yang rely on each other so that they can continue to exist, feeling a sense of obligation to never die because they're concepts that cannot cease to exist. Their teamwork is perfect, where very few can match them in this aspect, leading for them to perfectly make usage of their Noble Phantasm within combat.

History
Some time before his debut, Qin Shi Huang experimented with the concepts of, using two residents of Zhōngguó as a medium. He had used one of the test subjects as a medium for Yin, while the other subject was meant to be a medium for Yang. However, understanding the concept of Yin and Yang, he deemed it more beneficial to create an amalgamation of the two so that they would be able to access balance. The summoning was done via the usage of his Flaming Pearl, thus abiding by Jade Trumpeter's wishes and creating Assassin with a damaged Saint Graph.

Metropolis
Assassin made their debut during the Z-Team's voyage into Metropolis, holding onto a balloon and paying a visit to Chaldea while Yang was in control. He had immediately dispatched of a Demonic Polar Bear, by repelling it far away from him, and then walked towards the entrance of Chaldea as though nothing had occurred.

Class Skills

 * Permeation (?) - The sole Skill of Assassin, where it allows for Yin and Yang to swap between the host of the body. With this Class Skill, they are able to exist as a Servant with two True Names, as well as swapping their Parameters during the process, giving them a slight advantage over their enemies, simply because of how quick the process can be. Due to its unknown ranking, they have also shown to completely swap appearances whenever one is trying to take over the body. The biggest flaw with this Skill, however, is that if one of the two halves is defeated, the entire Servant is eradicated.

Trivia

 * Yin uses the design of Franziska von Karma, while Yang uses the design of Shelly de Killer. Both of these character designs are from the Ace Attorney series.