From Beast's Lair:
Based on the Doujin Fighting game, Melty Blood, made by the Doujin group, Watanabe Seisakujyo (now known as French Bread). This story is one of two side-story sequels occurring approximately a year after the 'good-ending' story of Arcueid from the original Type-Moon game, Tsukihime.

One year has passed since the 'Serial Vampire Homicide case' was solved by the deaths of Nero (Nrvnqsr) Chaos and Roa/Shiki Tohno. But now the rumors of serial murders are happening again. And so, once again, Shiki Tohno patrols the city to find this phantom killer. On patrol he meets--and fights--a mysterious woman named Sion Eltnam Atlasia; member of the church group 'Alchemist of Atlas', who seek to cure vampirism. But to do so she needs data from Arcueid, the last True Ancestor, to help her in her research. But this won't be easy: Ciel is also patrolling the city looking for the rumored killer, while Akiha has been acting strangely the past few days. Also, Arcueid hasn't been seen for awhile--could she be the killer...?