Dianoid

The Dianoid (ダイヤノイド) is a commercial building complex located in School District 15 of Academy City. Several advertisements were made during the novel series regarding its features. The building is described as a place for the rich and famous. It is used mostly as a shop, and is referred to as a fashionable date spot. It is soon turned into a battleground soon in the story.

Appearance
The building itself is made completely out of diamond, as suggested by its name - every wall, window, pillar, light fixture and even furniture is made of it. It is stated to be seventy stories tall. It is said to have toy stores that were specially opened as a Christmas sale, as stated by an announcer on the television.

Shinyaku Toaru Majutsu no Index
On December 1st, Kamijou Touma takes Othinus and Index to the Dianoid after Othinus saw an advert for a doll house made out of tiny bricks, which she wanted for a place to be safe from Sphynx. Kanou Shinka, using the assumed identity of Aihana Etsu, also travels to the Dianoid in hopes of finding out what happened to his friend Frenda Seivelun. Hamazura Shiage and Stephanie Gorgeouspalace are also carrying out a job there, and the other members of ITEM are there shopping. They are then trapped in the Dianoid together with the other customers when St. Germain seals off the Dianoid from the rest of the city with his carbon-controlling Chambord.

Trivia

 * During its announcement on television, the reporter mentioned that the highlight toy theme for the year is mini luxury. When a doll house that was made completely out of tiny bricks (stated to be about the size of a caramel) was advertised, a shrunken Othinus, who was watching the TV, stated to Touma that she wanted one for herself, leading to Touma's annoyance stating that he will make her one out of the empty snack boxes and tape.
 * This most likely was due to Sphinx 'playing' with Othinus, resulting in holding Othinus in his mouth. Othinus wanted safety from the cat and so asked Touma to buy one for her.