Index Librorum Prohibitorum's John's Pen Controller allows one to freely use any of the 103,000 grimoires in Index Librorum Prohibitorum. The user can use all of Index's spells even if she is not present. Each grimoire gives the user access to a specific spell and book in the library that they can mentally search through and activate. Each time a spell is activated it is accompanied with Index's voice warning and grimoire name. Grimoires are poisonous to the mind, however Fiamma seems to be immune to the mental decay and debilitating effects that result from reading a grimoire original.

“I suppose you could call it the external controller for John’s Pen, the safety device installed on Index Librorum Prohibitorum. It is a treasured item held only by the heads of the royal family and the Anglican Church. Of course, there’s the contamination from the original grimoires, so it’s really only a last resort. ...Didn’t you find it odd? No matter how much she wanted it herself, did you really think they would leave the Index Librorum Prohibitorum that held the 103,000 grimoires in the middle of that city of science with no insurance whatsoever? And it was the Archbishop that created this cruel system.” The second was what Index said herself. “Yes, I am the grimoire library...belonging to Necessarius, the 0th Parish...of the Anglican Church. My formal...name is Index Librorum Prohibitorum, but...as a nickname it is abbreviated to...kssssshhhhhhhh.” Index had been muttering expressionlessly, but she had suddenly started to shake unnaturally before she collapsed to the ground. “Index!!” “Oh, was John’s Pen damaged at some point? Well, it’s unfortunate that the body can’t be completely controlled, but it’ll still work out like this. ...If I modify the spiritual item a bit to increase its ‘output’, I can most likely manage to freely access the knowledge of the 103,000 grimoires.””
(To Aru Majutsu no Index Volume 18, pg 239)

Notable Grimoires
St. George's Sanctuary: A high class defensive spell which distorts space-time forming a barrier preventing oncoming attacks from reaching.

Dragon's Breath: A high class offensive spell that has the same power of the legendary dragon of Saint George. This spell produces a destructive beam of light while also transmutes everything it touches into 'Feathers of Light'. It was capable of destroying Academy City's Tree Diagram satellite in orbit and surpass the cancelling speed of Touma Kamijou's Imagine Breaker.

Feather of Light: An aftereffect of 'Dragon's Breath'. The feathers of light created possess unclear effects, but one falling on Touma's head was able to destroy the brain cells containing his memories.

Eli Eli Lama Sabachthani: A powerful anti-Christian spell which fires a blood red beam of light capable of easily ripping through Innocentius. It is powerful enough to overcome Imagine Breaker's negation and multiple beams can be fired simultaneously.

Baopuzi: A grimoire from China with a way to become an immortal written inside it. Within the book is the way to learn Rentanjutsu. It's said a person can create a miracle drug to cure any illness or curse using that technique.

Scarlet Stone of Pexjarva: 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: 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.

Weapon Grimores: Index has also displayed the ability to summon legendary weapons and artifacts and can create multiple copies in combat.
1. The Sword of the Harvest God Freyr: The sword of victory is wielded by the god Freyr. Freyr’s sword had never once been depicted as losing in Norse mythology. Drawing from that legend, the weapon fights on its own weaving its way through the gaps of its enemies defenses achieving victory. The speed of its attacks are capable of destroying Innocentius by wearing down its regeneration despite being supported by rune cards.

"Within Norse mythology, there was no legend in which that sword lost. Even in the final battle of Ragnarök, Freyr only lost because he had left the sword with someone else before the war began, so a means of defeating that sword was not recorded anywhere. Even Odin and Thor were defeated along with their weapons, but that sword alone was undefeated. Innocentius alone was not going to be enough. The giants would be quickly worn down and would be annihilated without being able to recover. If that happened, who would stop Index?"
(To Aru Majutsu no Index Volume 22, pg 33)

Momotarou: A grimoire that details a way to create an elixir of Immortality.

Moonchild: A grimoire that contains a way to summon a spirit using an angel's binding technique.

John Pen's Defense Mode: Index refers to this as her "awakening". Her speech becomes blunt and to the point and her voice becomes machine-like and toneless. It appears when Index's life is in a dire situation which makes seemingly immune to pain. Index's Controller can forcefully activate this mode. According to Index, she is incapable of magic, but in 'John's Pen's Defense Mode' she is capable of accessing the grimoires in her mind.
1. Spell Interception: Index 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.
2. Sheol Fear: Index's singing ability to form a 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 or when the intended target cannot hear it.

Crimson Wings: Red angelic wings that are sprouted from the back. They have enough power to destroy Innocentius and bypass it's regeneration without directly removing the rune cards that support it.

"A mass of exploding flame exceeding 3 meters in height appeared. It was in the form of a person. The mass of flames that burned at 3000 degrees Celsius was named Innocentius. Index’s head moved slightly to ascertain her target. Immediately afterwards, a great noise exploded out and Innocentius had already been blown away. The girl had swung the red wings growing from her back. With that alone, the giant god of flames was instantaneously ripped apart despite being supported by thousands of cards. It did not even have the chance to carry out its automatic regeneration. The burden received by Innocentius reversed the flow of energy and burned the cards black making them useless. That was the power of the grimoire library Index Librorum Prohibitorum. By freely wielding the 103,000 grimoires, she became the strongest defense mechanism for protecting that treasure trove of knowledge from those who would usurp it. However, Stiyl did not have time to calmly analyze all that. When Innocentius was blown away, it scattered in all directions and the explosive wind bared its fangs towards Innocentius’s user."
(To Aru Majutsu no Index Volume 21, pg 25)

Description of Innocentius's regeneration
"Kamijou Touma blew away Stiyl Magnus’s final trump card. As if he had stabbed a water balloon with a pin, the human-shaped fuel oil symbolizing the giant flame god burst into spray and scattered about the area. “...?” Kamijou Touma had no real reason for not taking his last step at that moment. It was simply that Stiyl was still smiling despite having his final trump card destroyed. That expression was enough to make him hesitate before carelessly taking that last step. The sound of a viscous liquid moving could be heard from all around. “Wha-...!?” As Kamijou took a step back in surprise, the black spray returned from all directions, gathered in midair, and reformed into a human shape."
(To Aru Majutsu no Index Volume 1, pg 65-66)

"Despite his confusion, Kamijou just barely managed to realize one thing. That mass of flames known as Innocentius was definitely reacting to his Imagine Breaker. However, it was being revived just after being annihilated. Most likely, the lag between annihilation and revival was less than a tenth of a second."
(To Aru Majutsu no Index Volume 1, pg 66)

“Attacking Innocentius will have no effect. Unless the rune engravings carved into the walls, floor, and ceiling are eliminated, it will revive as many times as necessary.”
(To Aru Majutsu no Index Volume 1, pg 67)

“With my introduction complete, I will return to my explanation of runic magic. Simply put, it is like a reflection of the moon in a lake at night. No matter how many times you strike the lake surface with a sword, it has no meaning. If you want to strike the moon in the lake surface, you must first turn your sword on the real moon floating in the night sky.”
(To Aru Majutsu no Index Volume 1, pg 68)

Did she mean that what stood before him was not the true form of the supernatural power? Was it something like a photograph and its negative, and it would it continue to revive unless he destroyed a different supernatural power that was creating the giant flame god?
(To Aru Majutsu no Index Volume 1, pg 68)