Purification

In Tsukihime, the Church's method of dealing with the undead.
Dead Apostles… beings which were once human, but became bloodsucking monsters. In order to return them to dust, a religious symbol that they were familiar with in life is required.
The process works by driving the natural law from when they were a human into the vampire's body, baptizing and restoring their flesh, then returning them to dust. The conceptual armaments required to perform the ceremony of forcibly opening the composition of the flesh and locking it into its original state are called “Keys of Providence.”
To put it simply, a crucifix would be a typical example.
However, a crucifix will only be effective on vampires that were originally Christians. If the official religion when they were human wasn't Catholicism, it becomes much more difficult for the crucifix to generate an effect.
On the other hand, if the vampire used to be a Christian, then even if the human under attack is not a believer the crucifix will have an effect on its own.
Of course, it goes without saying that the effect will be greatest if they are both believers.

Tsukihime Data Collection: Tsukihime Dictionary
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In Tsukihime, the Church's method of dealing with the undead.
Dead Apostles… beings which were once human, but became bloodsucking monsters. In order to return them to dust, a religious symbol that they were familiar with in life is required.
The process works by driving the natural law from when they were a human into the vampire's body, baptizing and restoring their flesh, then returning them to dust. The conceptual armaments required to perform the ceremony of forcibly opening the composition of the flesh and locking it into its original state are called “Keys of Providence.”
To put it simply, a crucifix would be a typical example. However, a crucifix will only be effective on Christians. If the official religion when the vampire human wasn't Catholicism, it becomes much more difficult for the crucifix to generate an effect. On the other hand, if the vampire is a Christian, then even if the human under attack is not a believer the crucifix will have an effect on its own. Of course, it goes without saying that the effect will be greatest if they are both believers.

Tsukihime Dokuhon Plus Period: Tsukihime Dictionary Revised