Wadatsumi

Wadatsumi (わだつみ) is a beach house located in a jellyfish infested beach in the Kanagawa Prefecture, found a few kilometers from Academy City. It is the primary setting of the Angel Fall Arc. The Kamijou Family Residence is not far-off from the beach, as taking the train would take a whole day to get there-and-back. In the original novel, the beach house is taken care of by Maou and his unnamed father. In the anime adaptation, the both of them are replaced by an elderly couple, but their appearances that they switch into, Misaka Imouto and Stiyl Magnus remains.

Appearance
In the original novels, the Wadatsumi seems to be a typical Japanese beach house. Like having tatami mats, which is carried on in the anime adapation. However, the first floor of the beach house is made out of wood, elevated slightly above the sands, as such there is enough space for a person to fir under it, as Hino Jinsaku and Misha Kreutzev can attest. The first floor contains the sole television in the house, and is used for public use.

In the anime adaptation, the beach house becomes fancier. It now overlooks the beach on top of a hill, and is now large enough to hold an arcade and separate hotsprings for the two genders. From the hill, one can see a scenic view of the nearby town and the ocean.

Oowarai Beach
Oowarai Beach (大嗤海水浴場) is the name of the beach that is near Wadatsumi. During the duration of the arc, only Index, Touma and his family are the only apparent guest in the beach, as jellyfish season came early and as such turning any potential guests.

The beach is fairly large, though it is poorly maintained as rubbish can be found in the waters, though this only applies in the anime adaptation, as the beach is not described well enough in the original novel.

Furthermore, the beach remains nameless in the original novel.

Angel Fall Arc
Touma is forced to go on a vacation at the urging of Tsukuyomi Komoe as a way to slightly curb the increased hostility of delinquents towards Touma after defeating Accelerator in attempt to gain prestige. Here, Index and Touma utilize the various facilities of the resort with his parents.

Touma later discovers after much trouble, that Angel Fall has been activated and that everybody's appearance apart from his and the spellcaster's have been switched. Here, Touma meets Kanzaki Kaori for the first time since losing his memories, as well as Misha Kreutzev, and discovering that his friend Tsuchimikado Motoharu is a spy in Academy City.

Eventually, Touma figures out that his father, was the culprit of Angel Fall out of sheer coincidence. However, Misha who is actually Archangel Michael (the angel who fell) tries to attack them, since he desired to return to heaven, since killing the spellcaster will negate Angel Fall. Kaori however, arrives and preoccupies Michael – who she confuses as Archangel Gabriel – while Touya and Touma try to find a way to cancel Angel Fall.

Angel Fall was eventually cancelled with the help of Motoharu, who used his magic to destroy the ritual location — the Kamijou Residence.

Trivia

 * Touma comments on the suspiciousness of the beach, since it can be roughly translated as Big Joke/Big Jeer/Big Laugh.
 * It may be a pun of Oarai Beach in Ōarai, Ibaraki.