Lambskin Parchments

The lambskin parchments (羊皮紙) are a set of occult parchments, found by Accelerator in Russia during World War III and instrumental to Fiamma of the Right's plans. They would prove instrumental in healing Last Order and introduce Accelerator to the magic side of the world.

Principles
It consists of a set of dozen sheets of parchment with eerie spells and magic circles written on them in old ink, with the words written in, but amended with small notes in at intervals. The contents are about what to replace and with what in order to activate a Roman Catholic spell under Russian Orthodox standards.

World War III Arc
The parchments are first contained in a briefcase handcuffed to a Russian soldier present on the same Russian military convoy train Accelerator and Last Order are hiding in, but Powered Suits from Academy City's forces attack the train looking for the briefcase. They manage to cut the handcuff chain, but Accelerator, thinking Academy City is after him, attacks and defeats them. The parchments are later found by Accelerator, who decides to keep them, thinking they are related to the "different set of laws" Aiwass told him about and that his best bet would be to get information out of the people that these papers were supposed to be delivered to. Accelerator also feels an odd sense of pressure from them, the same way he feels around Unabara Mitsuki.

Upon arrival at his destination, a destroyed Russian airbase, Accelerator deduces that this was the work of an underground organization from the Dark Side of Academy City and concludes that he should look into the organization that infiltrated Russia to get his answers, but before he can do that, he is attacked by Vodyanoy and twenty other magicians. Defeating them and realizing he fought an enemy using vectors and laws unknown to him, and thus might be connected to the parchments, he thinks of questioning them, but before he can, he is attacked by Misaka Worst.

After fighting him a second time, Kamijou Touma leaves Accelerator with a note informing him to look for "Index Librorum Prohibitorum" to inquire about the lambskin. Later, after reaching the Elizalina Alliance and examining the parchments, Accelerator can tell that it is some kind of manual trying to illustrate a story, but is struggling to figure it out, until a bodyguard of Elizalina tells him she could decipher it for him. He later meets her, and she confirms that she can decipher it, but that it would take time. Accelerator however just needed to know that the parchments could be deciphered, and asks Elizalina to focus only healing Takitsubo.

The lambskin is revealed to be the last piece for Fiamma of the Right to fill the gap between Index's knowledge of all magic and allow him to access magic of Divine origins. He sends Archangel Gabriel retrieve it. Although the parchments remained in Accelerator's pocket during their confrontation, Gabriel was able to retrieve the magical knowledge from them through its senses and relay it to Fiamma via their link.

Design Evolution
Since the parchments contained a song in the form of a magical aria, Haimura Kiyotaka designed the parchments to resemble a musical score and musical notes. The version seen on the back cover is the revised version.