Index Librorum Prohibitorum/Abilities

Abilities
Despite normally not being able to use magic, Index has a magic name, Dedicatus545, "The dedicated lamb protects the knowledge of the strong" (献身的な子羊は強者の知識を守る). As the vessel for 103,000 magical books, she is unable to use conventional means to cast spells; instead, she can only use abilities which intercept opponents' spells.

Perfect Memory
Perfect Memory (完全記憶能力): Index is capable of perfectly memorizing anything, which is one of the reasons why she was chosen as the vessel for the 103,000 grimoires, magic books that are poisonous to the mind. This made Yamisaka Ouma wonder if Index is even human.

Not only that, but she has powerful analytical skills, able to examine a 30 fps anime easily, as well as making her able to reconstruct an image on a surface, like a balloon or bottle, even after it is destroyed.

Abilities-related to being the Index Librorum Prohibitorum
Index also has abilities that require no mana whatsoever, for they are not of magic, due to the knowledge that she has from the 103,000 grimoires inside of her. This allows her to minutely to pin-point the weaknesses in the spells of others better than anyone in active combat, and later use it against magicians, such as what happened to Angelene, and her poor usage of her magic coinbags in their first battle.

Spell Intercept
Spell Intercept (強制詠唱 (スペルインターセプト) ) uses Notarikon codes, a quick Kabbalah reading method that uses only the first letter of a word, to hijack the spell formula that the caster has been conjuring in their head and cause the magic to go berserk or be outright cancelled. .

Singing
Singing is a fundamental part of Index's abilities. Using her knowledge she gets from the 103,000 grimoires, Index uses her songs to break down spells and things similar to them. For example, Index uses her singing to eliminate the virus that plagued Last Order's mind, which allowed the Imaginary Number District and Fuse Kazakiri to manifest in Academy City.

A specific form of singing, Sheol Fear (魔滅の声 (シェオールフィア) ) is an ability in the form of choir that points out and impeaches the contradiction of the basis of the religion or theory of magic that has been cast and causes a break down in the enemies mind. This can be bypassed if there are belief systems nearby, such as an Amakusa Christian near a group of Roman Catholics, or when the intended target cannot hear it, such as when the Agnese Force nuns jabbed their own ears to block off the sound.

John's Pen
John's Pen (自動書記</rb> (</rp>ヨハネのペン</rt>) </rp>) is referenced by Index as her "awakening." Here, her voice becomes machine-like and toneless. Her speech becomes blunt and to the point. It appeared when Index's life was in a dire situation, and seemingly makes her immune to pain. She cannot perform magic at this point, and it seems that it's only purpose is to take over Index's body, when she herself cannot do it, like an Automatic Secretary.

Defense Mode
According to Index, she is incapable of magic, however, when under John's Pen's defense Mode, she is capable of accessing the grimoires in her mind. It is unknown whether or not she was capable of performing magic before losing her memories.

After Touma negated the Collar symbol put inside her mouth that was meant to kill her, the defense mode activated. Her voice retains the machine like characteristic, and her methods in eliminating enemies is machine-like. While in John's Pen Mode, she was capable of using several very powerful spells:
 * St. George's Sanctuary (聖</rb> (</rp>セント</rt>) </rp> ジョージの聖域), a high class defensive spell which distorts space-time.
 * Dragon Breath (竜王の殺息</rb> (</rp>ドラゴン・ブレス</rt>) </rp>), a high class offensive spell that has the same amount of power as the legendary dragon of Saint George. This spell casts a beam of light at the target, destroying everything in it's path. It has been shown to have very long range, such as when it destroyed Academy City's satellite that housed the supercomputer, 'Tree Diagram', in outer space. The first level of this spell is enough to surpass the cancelling speed of Kamijou Touma's Imagine Breaker and the second level is enough to blow away Innocentius with ease. The after-effect of this spell is the Feather of Light.
 * Eli Eli Lema Sabachthani (神よ、何故私を見捨てたのですか </rb> (</rp>エリ・エリ・レマ・サバクタニ</rt>) </rp>) - Is a powerful anti-Christian spell which throws a powerful bloody-red beam of light.
 * Scarlet Stone of Pexjarva (ペクスヂャルヴァの深紅石) - This spell causes the bones in the target's feet all the way up to the knees to feel a deep pain started to swell up. This feels like the joints between the bones being forcibly stretched apart. This invisible attack seems to be coming up from the floor and seeps into target's body from there.
 * Sulfur Rain will Scorch the Earth (硫黄の雨は大地を焼く) - An area spell attack that makes around 50 arrows appear from above. These arrows strike down like guillotines, piercing and burning through the target. Just one arrow alone is enough to turn stone into dust.
 * During Index's stay in St. George's Cathedral while she was being restrained by Stiyl Magnus, she grows crimson wings, which are said to be angelic wings. With them she could dissipate Innocentius and blow his user away by just flapping them.
 * Index has also displayed the ability to summon legendary weapons and artifacts creating multiple copies of the same and use them to attack, all of them 'being able to suffocate the enemy just by floating in the air', some of the weapons mentioned are:
 * The Sword of the Harvest God (豊穣神フレイの剣) or Sword of Victory, the magic sword of the god Freyr from the Norse Mythology, which the legends said that if someone wise possessed it, it would fight on its own and bring about victory for its owner.

Information transfer
Index is able to use the knowledge in her mind to make a Gungnir lance. In order to recreate the phenomenon, a magician of great power, skill, and mental discipline is needed to focus its power. By transferring the necessary information to Leivinia needed to draw out the design of the phenomenon from. By singing at ultrasonic frequencies necessary to keep the weapon formed, this continually exposes Leivinia to the knowledge of 103,000 grimoires through the singing putting her constantly in danger of succumbing to them poisoning her mind. Interrupting Index's continuous singing however would immediately result in the destruction of the lance. If it successfully imitated the phenomenon of throwing lance, it would likely destroy the world.

Indeed, Index doesn't need to sing to transfer a thought into someone's head. She can use a high-speed incantation, likely Notarikon, by merely moving her lips.

Other abilities
In Shinyaku Toaru Majutsu no Index SS, Index is able to read the contents of the Book of the Dead, and accurately mimic the voice of the person for whom the Book of the Dead is written for. It allows her communicate its contents with tone and feeling that perfectly matches that of the mimicked person. However, due to the unique property of the Book of the Dead, a grimoire that is different for each person a book is written for, it is likely an intrinsic part of the book and not one of Index's abilities.