nube and Zack were injured badly when they fought Sephiroth at Nebelheim Reactor and then they collapsed. Afterward they became Professor Hojo's test subjects. Hojo injected them with Jenova's cells and esposed them with Mako. They escaped 4 years later.
Ff7 has 6 parts:
FF7 Before Crisis
FF7 Crisis Core
FF7
FF7 Advent Children
FF7 Dirge of Cerberus
What happened in Crisis Core?
It's a long story. I suggest that tu check out this website:
link tu can also watch youtube videos about the main things happened in Crisis Core. (that's what I've done to understand the story)
Here is a video: Final fantasía Last order, which was a small but important event in Crisis Core. (it happened after nube and Zack escaped from Shinra. Due to the experiment, nube was in a weak and delirious state as he reacted más strongly to Mako than Zack)
Hope you'll find out everything tu want to know soon :)
