This immense figure is Taran Zhu, a Pandaren, who shouts in offense- and expels the strange black-and-white effects from Rell, releasing three strange beasts that immediately fall over dead.  Rell tells the soldiers to stand down from the native, and cordially greets him- explaining that you are from the Alliance, and asking what it was that Taran expelled from him.  Taran replies that this is not the place nor time for an explanation, and that the strange things that appeared to overtake Rell are the direct result of the slaughter of the unarmed Horde troops.

Rell starts trying to explain, about how there is a war on- but Taran overrides him, saying that he understands, but Pandaria is not like other lands and is, itself, alive- so one should be careful of the energies wielded and brought.  He tells everyone to put their weapons away- and then leaves.

Rell is puzzled when you next talk to him- but at least he knows what needs to be done.  He offers two quests to you now.

The Cost of War is about returning to safety- apparently not only is the entire base aflame, but more and more shadow creatures are emerging from the ground around.  Rell wants you to help clear a safe route through the mess to the town, where he will join you.  En route, you are to kill 15 Sha Haunts and 5 Sha Harbingers.

Envoy of the Alliance, however, is the main quest.  Apparently there is a cherry blossom orchard North of the base, and beyond that is a small, somewhat hidden village.  Rell wants to seek quarters there, and tend the wounded before continuing on.  He therefore authorizes you to represent the Alliance in the town, and you are therefore to go to the town and meet the local leader.  He and Agent Mishka intend to meet you there when you arrive.  His hope is that the presence of a hero like yourself will make a strong positive impression on the locals- so head up to Paw’don Village.

Of the things you have to kill, the Sha Harbingers are by far the more dangerous- though capping even those are the strange rifts in the ground that litter the area.  These rifts constantly channel a steadily increasing debuff onto you whenever you’re in range, drastically boosting Shadow damage dealt to you- which is exactly the kind of damage the Sha deal when they attack you.  If you have any way to draw the enemies away from these rifts, then, you’re going to want to use it as much as possible.  The Sha Harbingers will charge you if you attack from a distance- but luckily, their charge does not stun you, only slow your attack speed.  Outside of that debuff and the charge attack, all the Sha really have to bring to bear is rather large amounts of Shadow damage, so there’s not a whole lot to be highly cautious of here.  Just keep an eye on your surroundings and try not to draw too many attackers at once.