The Festum are a silicon-based superorganism in Fafner in the Azure that seeks to assimilate all life in the cosmos.
Whether the Festum originated in this galaxy much less the universe is unknown. A Festum hive mind core (Mir) landed in Japan millions of yrs ago. This Mir was responsible for the evolution of apes into humans and it has fused with human DNA.
In 2098 AD Japanese scientist discover the ancient Mir. Then in 2114 AD, the Festum invasion of Earth begins led by a 2nd Mir which lands in the Arctic. They destroy all of Earth's satellites, devastate public infrastructure, and attack all the nations of the Earth. By the year 2015, the Festum have wiped out NATO and the UN Headquarters in NY City.
The next year, it's discovered that the people have Japan have become sterile which was brought about by a gas released by the Mir. Fearing that its a disease that will spread to the rest of mankind, the human race in 2118 nukes Japan (only Okinawa and half of Hokkaido survives). By 2120, the remnants of the nations' armed forces unite into the Human Army under the Neo-UN. It has become a three way war between the Festum, the human army (Neo-UN), and the ALVIS people of the island of Tatsumiyajima (the protagonists of the story, Japanese remnant).
In the year 2151, the ALVIS humans have been able to persuade the least hostile Mir to stop the war and live in peaceful coexistence with humanity. Eventually the ALVIS people are able to communicate with the least hostile MIR and cease hostilities between the two, the Neo-UN forces having been virtually annihilated by that time. The genocidal Mir was placed into hibernation. In the meantime they prepared they planned to convince the Space Festum to live in peace with humanity.
The objective of the Festum is to give all sentient life in the universe the benefit of assimilation. They have a hive mind with the Mir as the core, which is a crystalline mass. All the Festum are an extension of the Mir. Shattering the Mir, results in fragments that become Mir and their own hive mind. In the "newborn" stage the fragments are vulnerable to influence by non-Festum. There is greater variety among "newborn" fragments than the natural-born Festum. The most basic of Festum are approximately 120 m tall.
Festum are a psionically able species with a telepathic range of dozens of kilometres. They are able to create wormhole-like spheres which destroy matter and are used to teleport. Higher-level Festum create energy shields which destroy any physical constructs or projectiles that come into contact with the shield.