The Bottlenose Nebula's unusually high density of subluminal civilizations makes it a popular region for xenoethnologists, and this has been the case for longer than most of our superluminal civilizations have existed. One particularly notable set of academics is the Transition Protectorate.
Unlike most spacefaring species, the Transition Protectorate's progenitor species (known as Left Chiral CNO-4b) did not develop electricity, wheels, or any of what could be considered 'typical' industrial technology. They went on to not develop computers, robots, or radio.
Instead, they used their unusually adaptive genetic structure to restructure their bodies to perform these tasks.
And when it came time to travel through the depths of space, they restructured themselves into space ships.
Never developing high-energy physics, the LC CNO-4b never developed faster than light travel. Traveling at near light speed, they spread through the Bottlenose Nebula over thousands of years.
Initially surprised by the density of other sapient species, they quickly realized the power of the more typical approach to technology these species had. In particular, according to their own surviving records, the idea of a computer both terrified and mesmerized them.
According to their records, they also decided these fragile, subluminal species would never understand the LC CNO-4b.
'Never' is a strong word, and a small group of them decided to become something that could understand the other species, and could be understood by those other species. Becoming something new was what the LC CNO-4b did, after all.
But to become something they didn't understand? That was, according to them, heresy.
This faction, and the governmental agency they used to organize themselves, become known as the Transition Protectorate. Their fear of accidentally causing the subluminal species to become something else before the Protectorate understood what they were at the moment led for an extremely restrictive set of rules, shaping everything the Protectorate did.
The Protectorate studied other species as best they could. According to their own records, they only attempted to blend in with locals once before realizing they were hopelessly incapable of passing as something they did not understand. But they understood plants and rocks well enough, so they were frequently and literally underfoot as they studied these species.
After around a thousand years, the wealth of culture inherited from these species began to reshape the Protectorate even before they could say they understood it. However, the rest of the LC CNO-4b were all but destroyed by the spread of things like "music" and "dance": the rhythms and complex vagaries could easily disrupt focus and cause their bodies to malfunction unless they dedicated their life to studying them.
Therefore the LC CNO-4b were all but replaced by the Protectorate, which was now effectively trapped in a loop of having to obsessively study something they didn't understand just in an effort to survive.
Eventually the Protectorate seemed to give up on transitioning to something that could understand and be understood on their own. Instead, they decided to directly import impossible-to-understand technologies like "radio" and "computer".
The Protectorate had no understanding of how to operate these devices with appendages. After hundreds of years they gave up on using them as the subluminal civilizations did, and instead wired them directly into their bodies.
Many civilizations have suffered Axiom Decay after adopting extensive cybernetics without proper neural interfaces and cultural training... but of all of them, the Protectorate might be the most severe example. After all, they didn't even have a concept for what "cybernetic" might mean.
Collecting and implanting technologies from hundreds of subluminal civilizations led to an explosion of ever-increasing technological complexity. Although the Protectorate never really understood what these technological devices were, they could manufacture them with ease by changing their bodies to secrete them.
For around a thousand years, they simply tried everything. Trial and error on a massive scale led them to make technological advances the subluminal species never made... but it was never made with a purpose in mind.
And then they accidentally finished a subluminal civilization's attempt to create artificial intelligence.
This moment is perfectly clear in the records they left, because absolutely everything about how they recorded things suddenly changed. The Protectorate didn't really understand the AI, and the AI didn't really understand the Protectorate, but together they began to change into something new.
Over the next few hundred years, the Protectorate radically changed. They created vast planet-sized computer banks to compute things they didn't understand and hotly debated the nature of the universe, of culture, of life.
That's when their war began.
Led by what was evidently three different genres of music, the Protectorate split into groups, each of which had a different vision of the future. They turned their massive planet-scale computer networks away from analyzing existing cultures and towards creating new, fictitious cultural elements. These were "thought bombs" intended to derail the AI of their competing factions.
Although no bullets were fired, billions of Protectorate members died.
The winner of this war was the smallest faction, based around the planet Byssil. By focusing on creating cultural elements from the natural patterns of the universe instead of from life forms, they created elements which could not be correctly processed by entities attempting to use a biological framework for interpreting them.
Music derived from the Blowhole and other astronomical entities became Allebeth, a genre of music still widely appreciated today. The Protectorate's deadly reaction to this genre of music has not been observed in any other species.
The winning faction went on to accomplish their goal: The Transition Protectorate transitioned out of the universe entirely.
It's unknown if they went somewhere else, changed form, or simply dissolved. But if you visit the Bottlenose Nebula and turn on a radio receiver, you're sure to hear their music, echoing among the stars.