Introductory Article

What is the THF (True Hyperion Federation) Universe?

The THF universe takes place in a fictional galaxy cluster named Fortrais. This galaxy cluster holds 8 major factions, each capable of intergalactic travel, as well as some more minor factions which are either galaxy-wide scale or subgalactic in scale. Unfortunately, due to the sheer size of the world I am building, it is impossible to make up every single possible faction, alien species, war, technology, artifact and planet. The Milky Way alone (which I should point out isn't a thing in the Fortrais cluster) consists of around 100 billion stars and thats before taking into account that some galaxies could be larger - and there are hundreds of galaxies in the Fortrais cluster.

SRIA Side by Tankium

Above: S.R.I.A

Who are these precursor factions you keep mentioning?

Long ago, several alien factions have roamed the Fortrais cluster before the current factions. Among these are the Xadia Ancients, Rikavi Ancients, Cynar and more.
So why is this precursor 'archaeotech' so well-hidden and forgotten?
The answer is simple. The precursors are dead. They took all knowledge on how to use and manufacture this technology with them into their grave - leaving only the most powerful modern factions with mere clues to figure that all out.
But what killed all the precursors?
Good question. No one knows.
In fact, billions die in desperate attempts to find the answer to this seemingly basic question. But since the THF universe is explained with a largely out of character point of view, I can tell you. Being an omnipotent god has its perks.
There was an event that I call the Starsong Incident. This consisted of a continually expanding barrier of energy called the Lifeform Energy Barrier that killed everyone that touched it and blocked all forms of FTL. Everyone at the time made different attempts to escape the incident, all desperate of course. The results of this have left behind some highly intriguing precursor technology and megastrucures. As a testament to their engineering prowess, they still function billions of years later after all life in the cluster has been wiped out from the incident and re-evolved.
It all gets more complicated than that, of course, but not to worry because I have a full timeline written. ! Main Timeline

Sovereign Light by Tankium

Above: Sovereign Light - Class Advanced Cruiser

So what kind of aliens are there?

Many! In fact, I have made up more than 50 unique species. You will find everything between classical humans to aliens comprised of exotic states of matter and even species that can blur the line between machine and organism. One thing to note is that I count sapient AIs as a species in this case. Several 'species' of AIs exist as well.
One trouble that many factions have is to allow interaction between different species to happen easily and fluidly. How would a human communicate to a species that communicates through bioluminescence and cannot hear? They would also need to take the unique needs of each species into account. On the scale of galaxy clusters, who knows what species you could find? What if someone requires a surrounding environment in the thousands of degrees? How are they going to survive on a starship along with humans?
There are also benefits to this immense diversity. The weaknesses of one species is always covered by the strengths of another. Suons reproduce slower than humans do, but are not susceptible to the flow of electricity.

How do they get across these limitations?

Advanced Technology!

"Sufficiently advanced technology is indestinguishable from magic."
Lets talk about the Hyperion Federation (HF) specifically here - they are the most developed faction of them all (and you should probably read that article first, by the way) The HF uses Universal Translator technology, but that isn't the whole solution! The HF cybernetically enhances their people, allowing them to breathe in alien conditions as long as they are close enough. Thankfully, the vast majority of species can survive in these contitions with their cybernetics. They can also take a lot of weight off one's bones and allow people to withstand higher gravity than their species have evolved for.
But for a faction to survive in the THF universe, they would need to do more than just coexist (war counts as 'coexist' in this case). They need to develop technologies powerful enough to ward off the other factions nearby that probably threaten them with war. To this end, the HF uses antimatter to power their starships and has incredibly powerful laser-like weapons that create enough energy to compete with a Tsar Bomba - in a single second of firing time.
The HF is also a post-scarcity society. They have no money economy - and rely entirely on Replicators to fulfill their needs. These clever machines can '3D print' matter from Matter Plasma and construct (amost) any desired object.

There is one last issue I shall discuss here.

When you run such a massive star nation (or alliance thereof), the needs of that society increase exponentially.

This is where megastructures come in play. Everything from immense Dyson Spheres to Intergalactic Gates are commonly seen. There are also weaponised megastructures - such as Nicoll-Dyson Beams and the terrifyingly powerful Cypher Hyperquasar Annihilator. When you need to store an immense amount of information to keep your population - which is likely to be well into the quadrillions or sextillions - informed and happy, Matrioshka Brains are one potential answer. Megastructures come in all shapes and sizes, but I would argue that the term is relative. Space elevators are smaller than some starships or stations in sheer mass, but are considered megastructures. How? Because they are planetbound - and singular planets are quite limited in scale. some individual structures built on Paragon might even exceed the size of planets - and yet not be considered megastructures.