The year is 10k A.D., and in a system at the edge of the galaxy there is a space station. Station, as he calls himself, though referring to him as a male is merely a convenience, has been there for as long as he can remember, though he doesn't believe he can access any memory older than 5500 years. Occasionally he has seen vessels float within his sensor range, and has retrieved them in order to gain access to their records, databases, and technology. These ships come by rarely, the two nearest to each other coming eight years apart, the two furthest over a century apart. They are the unfortunate vessels that were unable to leave hyperspace, having missed every exit, natural and artificial, and having impacted the barrier at the edge of the galaxy, they floated for years, centuries, or millennia before being caught, most life on board having long ago died off.

Occasionally, during his down times, he has visions. Memories, historical records, entertainment files, he knows not what they are. They show a young man giving himself over to a medical procedure which will transfer his mind and memories into a ship's computer banks so that he could survive the journey through a hyperspace gate. The gates were a piece of alien technology which sent you into a dimension that humans had no natural defense against the effects of. Once on the other side, his body would be repaired or cloned, whichever would work best, and his mind would be reincorporated. That's where the visions end.

One day Station perfected a way to draw in ships from hyperspace, to drastically increase the odds of encountering vessels. A few months later, it drew in something that he couldn't remember every seeing before, a starship with people on it. Living humans. Though he saved their lives, they were trapped. No form of Hyperdrive he knew of could allow one to enter Hyperspace this close to the barrier.
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The only point of this will be to live in this system, aboard station, and, through the joint narrative, to answer the question posed in the title. What does it mean to be human?
You can be any kind of human you want to be, cyborg, genetically engineered, human-contiousness-downloaded-into-an-android, completely organic, more evolved, alien hybrid, whatever, as long as you can call yourself "human".
I am a bit worried that this is to serious for most people. Most of the RPs I've been in were far less serious and lasted for only short periods.