Sometime during Koridai's history, Ganon and his minions had invaded and taken over the island country. The island's five main regions were then left in control by Ganon's minions; Goronu, Harlequin, Militron, Glutko, and Lupay, and the conquered regions turned into the "Faces of Evil", giant mountains and structures in the shape and likenesses of their heads. Ganon's minions had also begun enslaving many of the islanders and turning them into monsters. Gwonam, a Koridian wizard, then quickly rushes to Hyrule by magic carpet to inform the King and Link of Ganon's siege. Although the King offers their aid, Gwonam explains that according to a written prophecy, only Link can defeat Ganon.
Gwonam and Link hurry back to Koridai. Link is told that he must fight each minion and reclaim their Faces of Evil. The hero ventures forth into these lands, where he battles many enemies and meets several Koridians who had managed to escape capture. On his quest, Link learns that Ganon had also captured Princess Zelda during his absence and held her captive under the effects of a sleeping spell. Link managed to locate her in Fortress Centrum, however this was an ambush staged by a disguised Goronu. Link also finds the Book of Koridai in the Shrine of Koridai, and learns from Aypo the reader that it is necessary to defeat Ganon.
Eventually Link defeats all of Ganon's minions, some of them twice, and journeys to Ganon's Lair. There, Ganon tries to persuade Link into joining him by offering to make "(his) face the greatest in Koridai". Link however defeats Ganon by throwing the Book of Koridai at him, magically imprisoning him inside. The real Princess Zelda is then found asleep in a chamber, and Link rings a nearby gong to wake her up. Gwonam then arrives to return them home. The island is promised to return to harmony, and Link is declared the Hero of Koridai.
The governance of Koridai is mostly unknown, as no ruling or authority figures, other than Ganon and his minions after their siege on the island, are encountered. The island's Fortress Centrum, however, may have been used as a base of military operation before being abandoned and subsequently taken over during Ganon's control.
- Main article: Rupee
Similar to Hyrule and other lands, Koridai's official currency is the jewel-like Rupee, referred to instead as "Rubies". Unlike other lands however, the value of Rubies vary slightly differently in Koridai as their colors are swapped; red is worth one, green is worth five, and blue is worth ten. Rubies are accepted at Morshu's shop, but are also notably used to power many of the items and power-ups that are found on the island.
Unlike Hyrule with its flat lands and varied regions, Koridai appears to be a mostly mountainous island. The island features multiple mountain peaks, many of which climb high above the ocean and tower all around the island territory. The peaks make the island's landscape very hostile, with most of its regions consisting of mountain passes, caves and tunnels, and rapid waterfalls that torrent down the mountain sides, most prominently in Spearfish Falls. The island is home to volcanic activity, with a large active volcano in the island center comprising of Firestone Lake and a smaller one local to Crater Cove. To the north-west is Nortinka and the neighboring Serigon Caves, the island's frigid regions covered densely in ice and snow.
The island appears to not have any towns or villages, either as the result of the island's difficult landscape or as a result of Ganon's take over. Despite its volatile nature however, several citizens make the island their home, and mostly live in caves, igloos, or in small houses scattered across the land. Several settlements do exist around around the island, however, most of these now inhabited by Ganon's forces. Small fishing settlements are found on the coastline of Crater Cove. Toyku Lighthouse stands in the western coast of the island. The only known shop on the island, Morshu's shop, is located in the Goronu area. The Harlequin Bazaar in the "Face" of Harlequin is an extravagant attraction that serves as a casino. The large castle Fortress Centrum stands atop one of the island's peaks. The Militron area is home to an armored military base. The Glutko area guards the way to the Shrine of Koridai, where the Book of Koridai is kept.
During Ganon's siege of the island, several of its regions were conquered and left in control of his henchmen. This is represented by the "Faces of Evil", mountain peaks and giant structures that bear angry glares in the likenesses of the minions that now control them, and are likewise named after them. In the south is the face of Goronu, Harlequin's and Militron's faces in the north-east, Glutko's face in the south-west, Lupay's face in the north-west, and Ganon's own Face of Evil in the center of the island.
Koridians are the humanoid populace of Koridai. They appear to be Hylians in that they have pointed ears characteristic to them. As the island appears to not have any towns, most Koridians are seen living in small huts or houses around the island, and others living inside caves, such as the Crone in Spearfish Falls. Ganon's minions have captured and enslaved most of the populace, leaving only a few remaining that now live in solitude. Apart from the Hylian-like Koridians, Fairies also inhabit the island, and live in a small Fairy Fountain located in Spearfish Falls.
Several generic, nameless Koridians also appear in the introduction cutscenes to Ganon's minions. They resemble men with short to medium-length orange hair. These Koridians are often met with morbid ends, as they are shown being turned into Goriyas by Harlequin after losing all of their Rubies, "hardened with fire" and transformed into Armos by Militron, eaten alive by Glutko, and having their souls replaced and turned into Moblins by Lupay. Those turned into monsters are then sent to fight Link.
- "Your Majesty, Ganon and his minions have seized the island of Koridai!" — Gwonam (The Faces of Evil)
- "These are the Faces of Evil. You must conquer each." — Gwonam (The Faces of Evil)
- "Koridai has fallen to Ganon and his evil friends! The gentle islanders are being transformed into blood-thirsty warriors." (The Faces of Evil manual, pg. 2)
- "Rumors are circulating that while you have been traveling to Koridai, Zelda has disappeared from the Palace! Could it be that Ganon has used his magical powers to kidnap her?" (The Faces of Evil manual, pg. 9)
- "Look, already Koridai is returning to harmony. The birds are singing! Isn't it beautiful? [...] As it is written, you, Link, are the Hero of Koridai!" — Gwonam (The Faces of Evil)
- "See how Harlequin captures Koridians?" — Gwonam (The Faces of Evil)
- "Not many left, Link." — Horgum (The Faces of Evil)
- "My husband gave me this. He's an Abominom now." — Alora (The Faces of Evil)