Itsuwa

Introduced in light novel volume 11, Itsuwa(五和) is a 16-year old girl who is among the members of the Amakusa Catholic Church.

Appearance
She is a young girl with purple chin-length hair in a bobcut with short fringes.

Her outfits consists of clothing worn such that much of her skin is exposed, though often not by her own choice. In volume 14 she was forced to wear those clothing because she had nothing else to wear after jumping into the river to save Touma, and in volume 16 the pants were designed by Academy City to make it seem to expose a lot of skin, but it's just fabric that look like skin underneath.

Her weapon is a Friulian Spear that can be disassembled and reassembled, for purposes of carrying it around without people noticing it.

Personality
She seems to have romantic feelings towards Tōma but due to her shyness, she was not able to act on them and convey them to him, she even say even if their Supreme Ponfit (Kaori) having feelings for Touma, she will never give him to her.

La Regina del Mare Adriático
Introduced for first time in the series, she appears alongside with other members of the Amakusa Church making a research about the remodelation of one of the Roman Catholic Church's artifacts, thats when she meets Touma in person after hearing from the others members Touma's prowess as facing 250 battle nuns on his own before he got the help from the Amakusa Church, Stiyl Magnus and Index; and all of them showing his respects towards him after hearing he also fought Kanzaki, saw her totally naked, received Nanasen and walked away alive.

Terra of the Left and the Document of Constantine
After Touma's involvement in the Amakusa Catholics and later, their agreement to aid Touma in Italy, when Touma was fainting for being strangled by the parachute strings after parachuting from a plane with Tsuchimikado, she rescues him before drowning. Amakusas were gathering info in France on what was causing this, and Itsuwa found Touma by pure chance since she didn't know about why Tsuchimikado and Touma are there. They join up before regrouping with Tsuchimikado. They go to nearby cafe to wrap things up before making a move. Itsuwa explains how popes used to be here at Avignon couple centuries ago, when France and the Vatican had a dispute and France was the victor.

They're spotted by angry mob before they could plan things out. This seems to be their attack against Touma, after spotting him drop off from the plane. They start moving toward Palais des papes. While dodging the mob to get there, Tsuchimikado contacts them. He was heading there as well, but wall of angry mob got too dense to pass by. They decide to cut the magical pipeline connecting Vatican and Avignon which allows the document to activate instead. This pipeline is flow of energy that runs through the globe, and they need either Itsuwa or Tsuchimikado to alter its path away from Avignon. Touma and Itsuwa end up at one of museums. Touma thought about breaking the link using the Imagine Breaker but was told by Tsuchimikado it might not work on the natural mana flow of the land, as there are exceptions to what the Imagine Breaker can negate. Just as Itsuwa is about to shut the pipeline using a magic circle made from common items such as water bottle, tour guide book, slippers and her panties, Terra of the Left attacked them with giant white guillotine blade, Touma managed to block it, and then both faced against Terra, she used the Seven Flashes, though he wires wrapped around him without any damage. Terra went through wall behind him and attacks, and the two can't do anything but to defend themselves.

While defending themselves, Itsuwa figured out that Terra's blade is made of flour, symbolising how bread is also the 'flesh of God' and the 'Fruits of the Earth'. After she does Terra explains with a smile that he can alter the hierarchy of things. He put himself above the metal wires so it didn't deal any damage to him. Tsuchimikado joins in and attacked Terra with his magical origami and a handgun while sending a note to Itsuwa and Touma to get away when the two collide. Before they do there's huge explosion outside, crumbling the museum wall. Academy City had sent their peacekeeping forces to attack Avignon.

Terra withdrew from the fight in order to secure the Document of Constantine and escaped because that's what the Academy City is here for. Touma and Itsuwa went after Terra while Tsuchimikado stayed behind to stall the Academy City forces.

When both, Touma and Itsuwa reached the Palais des papes, Terra appeared again and attacked, Terra exploded his blade and shot them out like a bullets at them, but Touma was unable to react but Istuwa pulled him away just in time and strikes at her. Itsuwa got injured instead and Terra scoffs at her for being dead weight but she answers to him that she's found out his weakness. Before she could speak Terra attacked and knocked her unconscious.

After a brief time when Touma already defeated Terra and was interrogating him about what Imagine Breaker is, a attack from HsB-02 blew the two away, she regained the conscious and founf Touma unconscious and damages caused by HsB-02. Parts of room has melted due to so much heat and covered with steam. She heard Accelerator speaking just as she start tending Touma, from where heat is still generated and no normal human being should be able to stand there. Accelerator is speaking with one of the higher ups of Academy City on the phone, telling them to send troops to come search for Terra's corpse and run DNA Tests to see if he's really dead. She stayed put not knowing if he's ally or foe, steam giving good cover for her and Accelerator leaves soon after to deeper part of palace. She found Accelerator, who can stand in flames like that, even more terrifying than Terra.

Aqcua of the Back's attack
In later events, she was assigned as Touma's bodyguard when Acqua declared he will come and take his life. When Acqua first attacked she failed to protect Touma, trying but failing to heal him with magic several time. After Touma was sent to the hospital she was despairing about her failure, before being rebuked by Tatemiya Saiji, saying to stop feeling sad and look to the future when Acqua will come and attack again, and prove to Touma that it was worth it for him to have protected her against Acqua. During the Amakusa Catholics' rematch against Acqua after Touma was nearly killed, she displayed a sudden change of personality, becoming full of tranquil fury that even the way she spoke changed after Tatemiya's words. Various male members of the Amakusa Church that saw this change rebuked Tatemiya for going too far with his words, talking without thinking just to snap Itsuwa out of her despair; now they will all have traumatising views and fear towards any woman that's in love.

World War III
When Lessar is flirting with Touma in Russia, On the battlefield at Dover Strait where the British are fighting the French, Itsuwa got a chill down her spine. Tatemiya Seiji asked her what’s wrong and she replied it’s nothing, but she has a bad feeling for some reason…

Abilities
A user of the Amakusa style, where its magic an be activated from everyday items like clothing, and has a wide range of uses. Due to the oppression to Christianity in Japan at the time of its founding, its magic have evolved to make sure it's hard to detect, incorporating magic with everyday life actions, and most users of the Amakusa style are more proficient than other mages at distinguishing minute magical traits in a spell.

More specifically her abilities that has been shown in the novels nclude:
 * Amakusa's Style Combat: Which she performs using her Friulian spear for single and melee combat, can perform battle formations which boosts up her speed and agility enough to equate Acqua of the Back.
 * 1) Nanasen: Just like Kaori does, but using her spear with thin strings.
 * 2) Healing Magic: Attempted to use on Touma in volume 16, but was negated by Imagine Breaker.
 * 3) Defensive magic: Which transfers part the damage she takes to her clothes.
 * 4) Forge Magic: Which improves her spear and endures it by the time passing. By adding layers of reinforcement, it turns the spear to a symbol of a 'Thousand Years Tree', which symbolizes the growth of plants and makes certain magic spells to be more potent over time.
 * 5) Anti-Divine Magic: Developed by the Amakusa Church merging Shintoism and Buddhism she, with help from the rest of the Amakusa, can use saints own energy to perform the Saint Destroyer(Seijin Kuzushi) spell. This spell is stated to only work against divine beings like Saints and does nothing to 'normal' magicians. Described in volume 16 as forcing the large magical energy that the Saint keeps in check to go berserk and self-destruct. In the same volume the first time it's used on Acqua it fails, due to Acqua's traits as part of the God's Right Seat in addition to being a Saint caused self-destruction o on him.

Trivia

 * Fans have speculated that Uragami, the Amakusa Catholic girl that Touma fought and saved from a fall in volume 7, may be her, the Amakusa warrior who was first introduced in Volume 11. If it is true, that may explain why she has a crush on Touma in the first place or if not a love at first sight. We'll just have to wait for season 2 of Index to see if it's her.