Nicknamed "The Serpent" due to his reincarnation abilities, Roa was a priest of the church who sought immortality. He deceived Arcueid into consuming blood hidden within a rose, triggering her berserk state and leading to the near annihilation of the True Ancestors. This act also transformed Roa into one of the most formidable Dark Apostles, powerful enough to defeat Altrouge Brunestud when she attempted to "teach him a lesson," as other Dark Apostles viewed him as an upstart.
Roa's original body was eventually vanquished by a coalition consisting of Arcueid and the Burial Agency. Since then, he has been continuously reincarnating. By the time of Tsukihime, Roa had already reincarnated 17 times, with each incarnation being destroyed by Arcueid as she sought to reclaim her stolen power and possibly exact some form of revenge.
For selecting the host of his next reincarnation, Roa has two requirements: the family must have high social standing to ensure he is born into luxury, and the body must possess significant potential. His last host was Ciel, hastily chosen, thus born into a baker's family but endowed with an extraordinarily high physical and magical potential. Roa can be considered a friend or acquaintance of Nrvnqsr.
(Source: Wikipedia)
