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 brown 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.

The Queen of the Adriatic Arc
...

Document of Constantine Arc
After Touma's involvement in the Amakusa Catholics and later, their agreement to aid Touma in Italy, Itsuwa helped Touma and Motoharu to take and destroy the Document of Constantine. She and Touma fought Terra of the Left who was guarding that artifact.

Aqcua of the Back's attack Arc
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.

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 and also can use thin strings like Kanzaki Kaori' Seven Flashes.
 * Healing Magic: Attempted to use on Touma in volume 16, but was negated by Imagine Breaker.
 * Defensive magic: Which transfers part the damage she takes to her clothes.
 * 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.
 * 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 which allowed him to evade the attack before reaches to him.

Trivia

 * Fans have speculated that 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.