Full name, Sion Eltnam Atlasia. An alchemist from the Atlas Institute, one of the three great branches of the Association.
Melty Blood’s guest heroine. Her trademarks are her purple uniform and long braid, and her weapons are Etherlite (a nano-scale filament) and the Barrel Replica (an imitation of the “Black Barrel”).
Though she hails from the disgraced Eltnam family, she excelled within the Atlas Institute, and was even awarded with the name Atlasia, which marks her as the Institute’s next director. However, she had long harbored doubts about her situation, and was troubled by the fact that she didn’t know what the problem was.
As a result, when the Church petitioned Atlas for help with a vampire hunt, the angst-filled Sion volunteered her services. She confronted the Tatari, one of the 27 Dead Apostle Ancestors, and was ultimately defeated. Afterward, while suppressing her own now-vampire body, she evaded pursuit from both the Church and the Association and tried to challenge the Tatari one more time, but…
Her personality is totally serious and logical, and having fun doesn’t come naturally to her at all. However, that doesn’t mean she’s incapable of it. Perhaps it’s more accurate to say she’s a chairman-of-the-committee type, who really does want to have fun deep down.
Though Melty Blood diverges into various routes depending on the outcome of each fight, in the majority of the endings Sion leaves town having awakened to faint feelings of love—her first love, in fact. Sadly, it was cut short before it even began.
An oddity among the Tsukihime heroines (who are, by and large, always at each other’s throats), she is capable of getting along with everybody, in her own way.
Her initial design concept was “an alchemist and a soldier,” which should be obvious just from seeing her in action. Her energetic movements are very fitting.
By the way, her miniskirt is so short you almost can’t even see it at all. If I’m not mistaken, this is what they call the “absolute territory,” yes?

Tsukihime Dokuhon Plus Period: Tsukihime Dictionary Revised