A medium sized cluster at the edge of asari space. It contains at least six systems and includes the asari colony world Illium. This cluster is sometimes known by the unofficial name of "Illium Economic Zone", a reflection of that world's importance as a port situated between the Asari Republics and the Terminus Systems.
- Tasale System: Beregale, Illium, Ponolus, Thail, Naxell.
- Lusarn System: Jontan, Euntanta, Doriae, Tarith, Xetic.
- Ondeste System: Zesmeni, Acaeria, Maisuth.
- Talik System
- Vantage System
- Zelene System: Nepyma, Helyme, Epho, Gaelon.
- Repina (Yelnerman's Point.)
The cluster was penetrated by Reapers during the Reaper War. A direct threat to Illium was foreshadowed by the loss of contact with Talik and Vantage, neighbouring systems projected to be avenues of approach for an invasion of Tasale. Illium's ruling Board of Governors made no formal statement concerning the Reapers - the nature and extent of their forces still being uncertain at this early stage of the war - but enacted a range of emergency measures, including placing the Nos Astra Exchange under a temporary freeze to halt panic selling, and entering talks with several private corporations in possession of military assets.
Several days later, Reapers transited the Tasale relay and advanced on Illium. The Board judged the Reaper vessels' threat too great to permit safe departure from the system, and ordered all civilian vessels grounded. Elements of Illium's Tasale Fleet engaged the oncoming Reapers - identified as Destroyer types and lighter units only - while the major cities projected as Reaper landing sites commenced evacuation.
Tasale Fleet's strength was insufficient to halt the advance, and some Reaper vessels breached the defensive line and began surface attacks. However, despite significant damage, and loss of life at some evacuation points, much of the population under threat were able to be moved to secure locations. Meanwhile, Tasale Fleet enacted the Board's contingency plan, abandoning attacks against Reaper warships in favour of precision WMD strikes against troop carriers. Although Fleet losses were high, the strategy succeeded in denying the Reapers the immediately available ground forces necessary to rapidly expand from their bridgeheads.
With a number of major cities, including the capital Nos Astra, now in Reaper possession, but the ground advance blunted, those areas to which populations had been evacuated were able to shore up their defences. Many smaller settlements fell under attack from orbit, and were quickly abandoned amid catastrophic losses, but the largest secure cities managed to mount sufficient anti-air and anti-orbit defences. Reaper ground forces consolidated their positions and began rebuilding the forces diminished by their troopship losses, scouring all contested areas of the planet for victims to convert to husks, and launching periodic raids against the remaining cities.
Nos Varda - a satellite city to Nos Astra, and the destination of its evacuees - became the de facto planetary capital during the siege, protected by heavy defensive installations, barrier projectors, and a combined force of Illium huntress cadres and forces of the Eclipse mercenary consortium, which accepted effective nationalisation for the duration of the war in exchange for lucrative concessions. Although Reaper forces based in nearby Nos Astra mounted constant small-scale probing attacks, and several large assaults (including one later dubbed the 'Battle of Nos Varda', which succeeded in breaching the city's barrier lines, threatened key military installations, and inflicted significant civilian casualties before being repulsed), comprehensive scouting and sabotage operations conducted by huntress/Eclipse forces prevented the Reapers from amassing sufficient husk forces to overwhelm the city.
Two years after the Reaper War, a general health advisory was issued by medical authorities on over a dozen planets in the Nebula, regarding infestation by Cirilek's Skindiver, an arthropod believed to be indigenous to Heshtok. The creature nests beneath the skin of other animals, and was spreading through adjacent clusters with alarming haste. Colonies of the parasite were reported throughout the Crescent Nebula, in the wake of increased relay traffic from the Nemean Abyss, originating in the Shrike Abyssal. Over 450 infestations were reported in three weeks, on nine planets.
A few months later, a slaver convoy in the Crescent Nebula was intercepted by asari military craft. Led by the cruiser Iluata, the asari task force seized the convoy and escorted them to the Athena Nebula for processing. However, when marines boarded the slaver vessels to inspect their cargo, they were surprised to find hundreds of slave-collared raloi. This turn of events sparked speculation that the Belon’s Rift relay must have been restored to working order - four other relays had been recently repaired, and the 96th Patrol Flotilla was dispatched back to confirm the situation in the Crescent Nebula. This led to contact being reestablished with Turvess.