The negative lifestream started when Sephiroth finally merged into the lifestream at the end of FF7 contaminating it, when the lifestream came to destroy meteor many ppl were exposed to the contaminated lifestream, infecting them with Geostigma.
I've yet to hear an actual confirmation on exactly what started the Negative Lifestream. I've seen debate that it was Sephiroth, but I've also seen points towards it being the remains of Jenova. If it was in fact Jenova's remains, then Sephiroth didn't create it. He just controlled what was there and manipulated her remaining cells in the survivors to create Geostigma, which led to more corrupted Lifestream. But I'll concede that I'm mistaken on this one if someone could provide a quote with the exact information. I'll look through the RF myself as well.
Eventually the negative lifestream will take over, choking/corroding the planet, the video i posted earlier was the bugenhagen explanation of the lifestream, everything on the planet is made up of the lifestream from every living thing, every deceased person, its a source of energy, power, destruction, magic, etc
This is pretty common knowledge. However, the Bugenhagen explanation in that particular video isn't relevant to power. All that segment explains is the results when the LS leaves the planet. He goes on to explain Spirit Energy, and its connection to life, but any relations to power are explained by others (Sephiroth explains materia, Cloud and Hojo explain SOLDIER, etc, etc.).
Once Sephiroth negative lifestream took over the planet, he can alter it at will, turning the planet into his vessel and sail the cosmos.. that was his goal.
Which he quite clearly explained in the film. However, he was unsuccessful in his attempt. He never absorbed it, and therefore never gained any power from the Negative Lifestream that would be useful in combat, just as he failed to absorb it in FFVII and didn't recieve the power he expected to from that.
Huh? The lifestream is power.. what do you think materia is originally made up of? What helped disintigrate meteor? What were those creatures kadaj summoned made up of? What is Omega WEAPON composed of? Having control over a good portion of the lifestream is having control over alot of power.
1) Again, moderately common knowledge. I never once said that the Lifestream didn't grant power. However, I did say that the video you provided has nothing to do with power, and it doesn't. That video is from the Cosmo Canyon model, which he used to describe the path of Spirit Energy from living creatures to the planet, and the results if that Spirit Energy were ever completely drained. The video had nothing to do with power.
Now, if you were to cite Sephiroth's explanation in Nibelheim, during which he explains the concept of materia, or if you cited the various explanations provided by Hojo, Cloud, etc, etc. in regards to its use as a physical enhancer for SOLDIER personnel, I wouldn't be saying that the example provided had nothing to do with power.
2) Having control over a good portion of the lifestream does grant power. However, Sephiroth has yet to have control over a good amount of Lifestream. He had very little control in FFVII, and the Negative Lifestream we see him summon was a storm that was cast over a moderate portion of Midgar/Edge. As someone said earlier, a mere portion of the actual Lifestream was capable of covering almost the entire planet. Even then, Sephiroth never actually used the Negative Lifestream for anything besides creating said storm, which didn't actually do...well...anything. Had he absorbed it as he originally planned with the Lifestream in VII, that might be the case.
I don't know the exact page number, but in the RF it says that they were trying to give him a divine, supernatural, and otherwordly appearance.
I've been looking over it, and I haven't been able to find any use of the terms "divine", "divinity," or anything of the sort. Otherworldy and Supernatural yes, but not anything about him being divine. But I'm in a rush, so I'll look more closely later.