I'd think that in the Mirror Universe, Nero would more likely be the "good" guy... so flip flop most of the story to make the humans the aggressors.
When the Terran Empire fell, the Romulans took advantage of the moment and seized Re-Unification on their own terms
Romulan military science, now with access to the considerable mental abilities of the Vulcans, makes progress in leaps and bounds. This is all great for the Romulans... but the cost to the Vulcans is very high. They are a subjugated species, beaten, abused. Think sort of how the Remans were treated combined with what the Romulans did to the Andorian telepaths in Enterprise. Vulcan "seers" are able to detect the changes to the Hobus Star which will lead to its immanent explosion and armed with this knowledge, the Romulans start a crash program to develop a technological counter to the threat.
Unfortunately, during final testing of the device an accident at the facility where the device was being assembled unleashed a black hole which destroyed the planet (Vulcan).
The only viable device remains onboard the Military Transport Vessel Narada, which was carrying an early prototype to Romulus for further study by the Tal'shiar. Incidentally, the device is HUGE, which is what neccessited the conversion of the Narada from a deep space mining vessel to begin with... When she arrives at Romulus, The Praetor dispatches Nero to the fleet yards to have his ship speedily upgraded, going as far to give him the Sword (from the Empty Chair) to convey the importance of this. Nero is now the only hope of stopping the Super Nova.
However, as the Narada prepares to use the technology she comes under attack by a small, but powerful fighter ship. The Jellyfish (possibly given a more sinister name) under the command of Emperor-in-Exile Spock (who had been fighting a guerilla war since he was forced to flee Earth) is hell bent on stopping the Romulans for using any technology he feels could be used to further subjugate the remaining Vulcans, and for revenge. This part doesn't have to entirely make sense, sort of like the plot holes in the JJ verse. Spock's old, and a bit nuts... so we just roll with it. Anyway, his attack causes both his ship and the narada to be pulled into the black hole and sent back in time.
When the Narada pops in, the Kelvin immediately opens fire. Unprepared, and still reeling from Spock's attack, the Narada takes significant damage. Believing the Narada to be disabled, Captain George Kirk - who was promoted to the position following the assassination of the Kelvin's previous commander - contacts the Narada and orders her surrender.
Nero refuses, and attempts to disable the Kelvin's weapons while bringing her under tow with a tractor beam. The rest of the scene plays out like it did in the movie, with the Kelvin ramming the Narada and the escape by shuttlecraft. Oh, and George, simply LOVES Tiberious for his son's name... but his wife wants James instead.
Young Kirk behaves about the same as his counter part, only he's more arrogant and cruel. Spock's about the same... However, while he gets beaten by Vulcan children because of his human mother its far less public, infact, the children fear reprisals because by this time Vulcan has been subjugated by the Terrans.
Both Eventually make it to Star Fleet. Kirk cheats on the Kobayashi Maru... and...
Nero and his crew escape from the Klingons, destroying 47 Klingon cruisers. Realising that he has altered the time line, possibly to the detriment of the Romulan Star Empire, Nero sets course to Vulcan. His plan is to use the ships mining equipment to extract a rare ore to rearm the mirror Red Matter technology, he then intends to use it to eliminate the Hobus star and then use the black hole to go forward in time to fix the timeline. (either way, if he fails, Romulus is safe)
Starfleet sends a small fleet to Vulcan to eliminate Nero. Terran technology has advanced almost identically to the other universe, only all the ships have the neat Terran Empire hull markings and are designed a bit more aggressively (more weapons.)
And thats all I can think of right now...
