Mitsuari Ayu

Mitsuari Ayu (蜜蟻愛愉) is an antagonist who appears in Shinyaku Toaru Majutsu no Index. A Level 3 esper with the ability Mental Stinger, she bears an immense grudge against Shokuhou Misaki, who was chosen over her to be developed to Level 5 and was saved by Kamijou Touma when she wasn't.

Etymology
Her family name, Mitsuari (蜜蟻), means.

Appearance
Mitsuari Ayu has long, wavy, chocolate-colored hair, apparently as fluffy as cotton candy. She has smaller breasts than Shokuhou Misaki but apparently has more beautiful legs than her, more than just long and slender. She wears a special, dark suit, resembling a racing swimsuit, with similar gloves and boots.

Personality
Due to being not being saved by Touma due to Shokuhou Misaki, who was saved by him and was also chosen over her to become a Level 5, Mitsuagi bears an immense grudge against Shokuhou Misaki, to the extent that she wishes to steal the happy memories that Shokuhou has of him for her and her alone.

Background
In the past, Mitsuari Ayu and Shokuhou Misaki were found by Tree Diagram to both have the possibility of reaching Level 5, possessing abilities with a near identical basic theory and scope, though they would plateau at Level 3 under standard curriculum. The higher-ups decided to prune one and focus on developing the other. Following the Parameter List, they chose to focus on Shokuhou Misaki, with Mitsuari Ayu being kept as a back-up in the event of her death.

A year before the current year of the Story Timeline, Mitsuari Ayu had encountered Kamijou Touma. At that time, her circumstances had driven her to consider suicide. When she was about to go through with it, she sent a message to Touma, hoping that he would save her. However due to bumping into Shokuhou Misaki at an intersection, Touma lost his phone and as such was unable to reach her in time. Though her suicide attempt at Ground Geo failed, Mitsuari was drawn into Academy City's dark side and came to resent Misaki not just for stealing her chance to become Level 5, but also for being saved when she wasn't.

Abilities
Mitsuari's Level 3 ability is Mental Stinger (心理穿孔 (メンタルスティンガー) ), which operates in a similar way to Mental Out. Originally thought to manipulate the brain by controlling bioelectricity, it actually does this by manipulating moisture, controlling the distribution of fluids and the secretion of chemicals in the target's brain. Instead of directly controlling bioelectricity, it changes the conductive efficiency by controlling the fluid acting as a catalyst for it to flow through - as such, the ability doesn't work on espers that directly manipulate their bioelectricity such as Electromasters, though it is speculated that this can be overcome with an increased output. Abilities of a similar nature are also capable of resisting it. Similar to Shokuhou Misaki's use of remotes for Mental Out, Mitsuari Ayu sets targets for Mental Stinger with cameras and her fingertips.

Under certain circumstances such as extreme anger, the ability can go out of control and cause an explosive phenomenon similar to freeze-drying that creates a territory that can cause any living being within it to crumble like dried paper mache.

Equipment
Five Over OS (Outsider) - Modelcase Mental Out (ファイブオーバーOS(アウトサイダー)): Like other Five Overs, this is meant to reproduce a Level 5's power with pure technology, though the OS (Outsider) indicates that it exists outside the mainstream method, using methods different from a Level 5's power to produce the phenomenon resembling it. In this case, magnetically controlled monitor dust is distributed across an area and used to alter the appearance of the target's surroundings, using that twisted information to influence their mental state and memories. The device is still a prototype and has plenty of problems remaining, hence why it hasn't been mass-produced.

The base unit is a spherical device, taller than a person, with tentacles extending from its bottom half, resembling an artificial octopus. It is constructed from an artificial fat called Designer's Gel which is capable of changing shape. It has numerous large eyeballs on its surface, which roll and blink, perhaps due to the magnetically controlled monitor. '''Five_Over (Out_Sider). Modelcase_“MENTAL_OUT”.''' is written on the side of its tentacle. The Outsider can also take the shape of a large wearable suit, forming a body that should weigh around 300kg were it real.

The magnetically-controlled monitor (磁性制御モニター) that is used by the Outsider primarily consists of colored powdered dust, which is scattered throughout the target area and controlled via magnetism. It is capable of changing in real-time, altering the surroundings around the target to influence them. An example of this would be producing images of insects to induce revulsion and fear, or an eyeball with a gaze that paralyzes those that see it, much like Medusa in Greek Mythology. It is even capable of creating sound by rubbing together like cricket wings. However this system requiring a network of multiple viewpoints other than that of the user to perfectly overwrite the surrounding area in real time, which can be used by an enemy to manipulate the Outsider by feeding it with malicious information.

Five Over Modelcase Mental Out (ファイブオーバー モデルケース・メンタルアウト): Mitsuari's trump card against Shokuhou, a machine which is supposed to recreate and surpass Mental Out using technology. However this particular machine doesn't strictly fit the definition of Five Over as it doesn't contain anything to reproduce an esper ability using technology, instead containing 8000 output devices, with the intention to have Shokuhou Misaki placed inside and her power drawn out forcefully, in order to acquire the sample data to complete and mass-produce it, as well as to crush Shokuhou's mind with her own power. Resembling a scorpion wasp, its main body is 4m long with six legs and thin wings 8m long when extended. Its abdomen is translucent and filled with anesthetic conducting fluid, meant to contain a human body. It can be programmed to act automatically.

Strobila (ストロビラ): A device intended to manipulating the mind without interfering with the brain. It is consists of a very small plastic core with a long fiber that leads to the subject's heart and affects the secretion of hormones. Strobilas were installed in Shokuhou and Mitsuari's Outsider body as decoys.

Design evolution
Mitsuari Ayu's character design is basically the rejected initial design for Shokuhou Misaki, with a few changes to her expressions due to her psychotic 'yandere' tendencies. According to Haimura Kiyotaka, rejected designs are normally locked away however the story in this case was written using the concept of an unfortunate girl who could not become Shokuhou, allowing that rejected design to be made into a character.