Nicknamed "The Serpent" for his reincarnation ability, Roa was a priest of the church that sought immortality and tricked Arcueid into drinking blood hidden within a rose, causing her to go berserk and wipe out almost all the True Ancestors, and also turning Roa into one of the most powerful Dark Apostles, to the point where he was strong enough to defeat Altrouge Brunestud when she tried to "teach him a lesson" as the rest of the Dark Apostles saw him as a upstart. His original body was finally defeated by a coalition comprised of Arcueid and the Burial Agency, and he has been re-incarnating ever since then. By the time of Tsukihime he has already re-incarnated 17 times and been destroyed by Arcueid each time as she seeks to gain her stolen power back, and perhaps to achieve some measure of revenge. Roa has 2 requirements for choosing the host of his next reincarnation, his family must have a high social standing so he would be born into luxury, and a body with a high potential. His last host was Ciel, who was chosen in haste and thus was born into a bakery's family but instead had a body with an extremely high physical and magical potential. Can be considered a friend or acquaintance of Nrvnqsr.

(Source: Wikipedia)