Tatsue

Say, I look dead t'you? Tatsue ████████ is a Master of the Shattered Timeline Great Holy Grail. Summoner of Saber of Black, she later contracted Saber of Red as the girl lost her original Master.

Black Team

 * Dante

The first servant she summoned, Saber of Black. Initially, she hit it off very well with the man, his carefree nature and tendency to take things head on meshing well with Tatsue's reckless pursuit of a fight or distraction from her day to day life. However, he decided to sever their connection shortly after Tatsue contracted with Saber of Red, touching on her trauma of abandonment and her view of relationships being constantly fragile and temporary.

To his death, she viewed the Servant with spite and hatred, neither reconciling nor understanding the man to the end.

A strange relationship, opened with Tatsue's dismissal and refusal to cooperate with the majority of Black Team, neither staying in the faction's base nor communicating with any of its members.
 * Yatsuko

This only worsened after Tatsue defected and Yatsuko was later kidnapped, the delinquent taking it upon herself to interrogate the girl personally and breaking a few of Yatsuko's fingers in the process.

However, upon reaching the new world, they've had a strangely amicable experience, Yatsuko forgiving Tatsue for her earlier actions and striking up a conversation on their pasts.

Archer of Black is easily one of the individuals Tatsue holds the most enmity towards, nearly all of their interactions ending in verbal or physical conflict. On his end, he despises her defection to Red Team and general mannerisms- on her end, she finds the cloaked individual a coward and nuisance, someone whose methods wear her already thin patience to shreds.
 * Robin Hood

Little to no interaction with the Half-Phantom to date. Certainly not a result of both being characters of the same player.
 * Youmu Konpaku

Little to no interaction, up to the man's death.
 * Hideki

Red Team
The second Servant Tatsue contracted with, Saber of Red. Had a very touchy opening relationship with the girl, driven by a measure of pity and her compassion for children due to the Servant's appearance. Over time they argued frequently, Neptune's chipper nature clashing with Tatsue's more pessimistic outlook and abrasive personality, but began to gain a measure of respect for one another.
 * Neptune

At the time of Neptune's death, Tatsue had just begun to relax around the Servant.

Magecraft
The runaway heir of a semi-prominent magus family in the east, Tatsue's raw magical talent is actually above average, with good quality and an average quantity of magic circuits. However, her status as a runaway meant that she had no training in the usage of her circuits, and in fact was not even fully aware of her status as a magus. A portion of her family crest is embedded across her back, unused and dormant due to its irregular nature and Tatsue's inexperience.

Reality Marble
Her actual execution of magecraft is instead carried out through the use of her reality marble, formed as survival mechanism and result of her warped mentality throughout her adolescence. A world resembling the crime infested alleys and dark corners of her home city, it draws off of the Second Magic to search and connect to a specific target across different universes- Tatsue herself.

Once it has found a version of Tatsue, it then 'layers' and 'melds' it onto the original version of herself, using the attached layer to the original Tatsue's maximum benefit. Practically, injuries and environmental conditions that would be undesirable are offloaded onto the attached layer, where as the physical capability of the layer and sheer mass of the layer are readily available to the original. Shoot her, and the reality marble will either steal mass to immediately heal the wound, or offload the gunshot onto the layered version of herself before disconnecting it from her, while her own attacks will hit with the strength and weight of however versions of herself are layered onto her. Much like a filter or sieve, even older or non-physical effects such as curses can theoretically be purged from her body in this way, the alternate version of herself melding and taking on such effects before being disconnected from her.

This effect is entirely limited to Tatsue herself by default, but by deploying the reality marble she can apply a limited and reversed effect onto those she thinks of as hostile, 'layering' and 'melding' alternate versions of an enemy with wounds, diseases, or conditions that are undesirable onto the original to affect their combat capability and drain away their vitality. I.e., an opponent could be entirely untouched yet feel the pain and reduced strength of a broken arm. Depending on the circumstances, an opponent could die from these effects without Tatsue touching them, but unlike her personal application of the reality marble more extreme effects applied onto an opponent generally cost more prana and can be affected by the target's resilience to magecraft.