Northeastern Matoran universe
In existence, merged into Noctia Nui
Gekkak Nui was a Noctian Island island formerly in the northeastern region of the Matoran universe. Following the Noctian Island Relocation, it was fused with the other Noctian Islands and moved to Noctxia Magna.
Gekkak Nui was created along with the rest of the Matoran universe as a part of the Noctian archipelago. Its original inhabitants were Reptisapeans and Matoran, and from the beginning, the inhabitants squabbled heavily with their neighbors on the adjoining islands, leading to several minor conflicts. However, these conflicts were rendered moot when Ehlek of the League of Six Kingdoms conquered Gekkak Nui during the Barraki's early campaigns.
After the fall of the League, Gekkak Nui was united with the rest of the Noctian Islands by the Enforcers of Noctian Reign, leading them through a period of turmoil during the Barraki Islands War. While the war was notable for helping the archipelago cement itself as a weapons powerhouse, most weapons-manufacturing facilities were concentrated off of Gekkak Nui's shores: the island instead took its own route, focusing on building a navy to rival any other.
The development of the navy was cut short after the end of the Barraki Islands War, which was followed by many millennia of minor conflicts and cold wars with other islands, most of which were quelled by the Brotherhood of Makuta before they could escalate. This eventually led to the Brotherhood becoming confident in its supremacy, and it began to become lax and interfere less by 25,000 AGC.
Coincidentally, it was around this time that a small and previously unknown criminal organization rose to power on the island known as Dark Talon, which began to orchestrate larger and larger raids. Aided by the combined forces of other illegal factions, which were all quickly absorbed, it grew in power until it was able to buy the vehicle- and weapons-manufacturing companies instead of having to raid their factories.
The efforts of the island's Makuta, Krakanus, were relatively unsupported by the Brotherhood of Makuta until the Enforcers of Noctian Reign were nearly overrun; by the time it sent out a defense force, it had driven the Enforcers off the island and gained the backing of the Dark Hunters and several major Xian manufacturing firms, which wished to help install a more tolerating government on the island. It was at this point that the organization's leader officially declared war on the Noctian Islands, and set out on a campaign of conquest with Gekkak Nui as his main base.
The war continued for years, with neither side making a major breakthrough until the resistance managed to crack Dark Talon's communication codes and trick trick several different competing army commanders into believing that they had learned the location of the resistance base. While the bulk of their armies collided spectacularly on Veii-Nui, the resistance fighters launched their own attack on the relatively undefended Talon headquarters and bombarded the base mercilessly from the sky, killing the ruling council and then proceeding to reclaim the island as their own.
Gekkak Nui is unusual among the islands of the Matoran universe in that it is mostly jungle, with a thin strip of surrounding coastline before reaching the open sea. This jungle, though largely referred by the Reptisapean inhabitants, has been cleared out little and remains tightly packed, making travel on the ground virtually impossible. Instead, most travel between settlements is accomplished by airship; due to the impracticalities of long-distance airship travel, though, most travel off the island is done through ships.
The island is cut in two by a strait which covers a former major depression in the region, flowing south to north. It is joined by several major freshwater drainage basins along its length, the land nearby being mostly boggy or marshy, with some exceptions. This strait serves as a shortcut for many passing between the Southern Continent and the Noctian Islands, making its shores a major source of commerce. Most of the major Matoran settlements lie along its boundaries, comprising nearly half of the island's total population.
To the west of the island lies a large desert, where there was once a series of inland lakes, which later drained out after geologic uplift in the region. The river which connected it to the strait is now a canyon. Both the desert and the canyon have been colonized by Matoran, and are harsh but more accessible than the jungle area.
The remainder of the island's inhabitants reside along the shorelines. Given its relatively close proximity to various prominent islands, there are many docks along its shores, including many belonging to separate factions. However, the area in between it and Gaakhu Nui is difficult to navigate, and sailors risk death by taking the "Passage of the Dead." For this reason, the location known as Makura Bay has been unofficially dubbed "Shipwreck Bay."
Following its merging into Noctia Nui, the majority of the northern and eastern coasts has been pushed against the other Noctian Islands, causing the raising of a mountain range. The other shores remain intact, however.