Seventh Holy Scripture

The conceptual armament that Ciel is authorized to carry. An iron hammer created by Christianity in order to renounce the heretical doctrine of reincarnation.
…Although, if reincarnation didn't really exist then it seems like it would be kind of unnecessary to prepare an anti-reincarnation weapon, right?
Originally created by felling a miraculous beast said to consume souls, then using its horn as a key. The surface of the horn is inscribed with tightly-packed complaints about how “reincarnation is really lame.”
It was sanctified over the course of many years, but eventually fell into Ciel's hands.
“A horn!? That's not practical at all. The higher-ups are totally out of touch!”
Unable to hold herself back, she set about improving it.
At any rate, since it's been almost a thousand years since it was first created, it even has an elemental living within it… though the essence of its personality may have been a bit warped by Ciel's remodeling.

Tsukihime Data Collection: Tsukihime Dictionary
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Ciel's conceptual weapon. The iron hammer of reincarnation judgement. More than 1,000 years have passed since it was first created, and a spirit resides within (the figure you see when Ciel appears is the spirit). The spirit is called Seven, and she takes care of a wide range of things for Ciel, from sewing to being the target of Ciel's stress relief. The spirit is also called Nanako (refer to Kagetsu Tohya for details).

MB Official Strategy Guide: Melty Blood Glossary
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The conceptual armament that Ciel is authorized to carry. An iron hammer created by the Church in order to renounce the heretical doctrine of reincarnation.
It was created by felling a miraculous beast said to consume souls, then using its horn as a key. The surface of the horn is inscribed with tightly-packed complaints about how “reincarnation is really lame.”
Since it's been almost a thousand years since it was first created, it even has an elemental living within it.
It was sanctified over the course of many years, but eventually fell into Ciel's hands.
“A horn!? That's not practical at all. The higher-ups are totally out of touch!”
Unable to hold herself back, she set about improving it, and because of that the Scripture's elemental ended up having the essence of its personality warped.
Before Ciel remodeled it, it was only effective against spiritual entities. Now, however, it has been transformed into a lump of iron that can pound a vampire to death with its physical attack power alone. It has a gross weight of 60 kilograms, and a maximum weight of twice that with optional attachments. It's a… Gatling scripture!?

Tsukihime Dokuhon Plus Period: Tsukihime Dictionary Revised
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Ciel's Arc Drive.
The conceptual armament that Ciel is authorized to carry. Although it is called a scripture, it's actually an enormous pile bunker.
An iron hammer created by the Church in order to renounce the heretical doctrine of reincarnation. Over a millennium has passed since it was first forged, and there's even an elemental dwelling within it, but…
Before Ciel remodeled it, it was only effective against spiritual entities. Now, however, it has been transformed into a lump of iron that can pound a vampire to death with its physical attack power alone. It has a gross weight of 60 kilograms, and a maximum weight of twice that with optional attachments.
During Ciel's Arc Drive, she drives the stake into her opponent. Afterward, what is ejected from the magazine is not an empty cartridge, but pages of the holy scripture. For vampires, this is no different from being directly injected with the holy scripture itself. There is no doubt that it is a surefire “Immortal Killer.”

MB Act Cadenza PS2 Manual: Tsukihime Dictionary
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