(This takes place in the headcanon world of Gaia, which I and several other amazing authors have been building for over two years now)
The Chimeran virus began in in the northern kingdom of Boletaria and spread rapidly through the country. We didn't know how it spread, or how fast. All we knew was that in weeks, Boletaria had initiated a complete information blackout, and thousands were screaming on the other side of the border, trying to escape the onslaught. Even our own colonies in the north vanished without a trace
Then it turned southwest, sweeping through the Zebra kingdom of Zecca, and pushing past the Neophyte river and into the Iron Kingdoms. We thought we were safe behind our massive gates and large mountains, until the Chimera broke through into the northeastern Areyths. They had breached into the Eternal Forest, desecrating it's sacred groves. For a while, we believed our advanced armies would push the Chimera back, but when the majority of Areyth Nyaar's Dawnguard were lost, we turned to our closest surviving ally.
Equestria deployed five thousand Storm Rangers, with Warjacks and Stormguard heavy infantry to support them. They were as unprepared as we were in the beginning. None of them knew what they were fighting, their government censoring information on the Chimera to prevent rioting panic.
Among those soldiers was an old friend of mine, Lord Commander Ossyan Metalsmith. He came out of his early retirement when he discovered something was wrong in our country, as his family hails from here. Nopony has seen him since the end of hostilities here in Ios, but here what follows are the records of his last sightings
The air over the Ethrunbul Mountains was thick with clouds, which was normal. The elves of Ios had long ago enchanted the range to keep Pegasi from flying through them into Ios. Anyway, the cloud layer was making the gunship shudder every couple seconds.
Ossyan was silently gripping his harness, the half elf Lord breathing deeply through his nose
"Problems commander? I wouldn't of thought you'd get air sickness sir" a Ranger across from him joked
"I don't fly often Firepot" Ossyan managed a smile at the Ranger. Firepot was a relatively new recruit to the Storm Rangers, and it showed in his personality. He was still the cocky attitude of a greencoat, untouched by the horrors of war. Ossyan was almost saddened by the fact that that was about to change "In fact, this is the third time I've ever flown anywhere"
"That's gonna change sir, the word is we're going in, helping the knife ears like you, then moving on to the Iron Kingdoms" Firepot smirked "Didn't think we'd ever be the ones riding to the rescue of the Latins"
Ossyan couldn't help but chuckle "Can't say I ever thought it'd happen either. I remember when we were afraid of their predecessors coming over the mountains to conquer us"
"That's the spirit sir!" Another Ranger laughed "From the conquerable to the conquerors"
"We aren't taking territory you idiot" Firepot snorted before laughing
The gunship shook again as the airfleet broke through the cloud cover into Ios
Ossyan smiled, undoing his harness and standing up "Alright! Ladies and gentlecolts! Welcome to Ios! Command says we're being dropped by Areyth Shyeel, meaning we'll be there in about ten minutes! I want all of you prepped and ready for a dustoff in five! Move it ponies!"
The Rangers quickly unstrapped and began gearing up. Rifles were loaded, grenades armed, machine gun harnesses put on. Within five minutes, the platoon of forty Storm Rangers was ready to go. They were being sent to the fortress of Areyth Shyeel, where they would oversee the transfer of a weapon that could turn the tide of the war, something that the Equestrians couldn't hope to recreate. As soon as they landed, they came under attack by the Chimera, the creatures rushing through the hail of gunfire emitted by the Rangers.
"What the hay are those things!?" Firepot shouted over the thunderous sound coming from his machine gun
"I don't know! But there are too many, we've got to fall back!" Ossyan roared, pulling the platoon back. Soon, the creatures were gone, leaving the soldiers alone in the streets of Shyeel, outside the mighty fortress.
"Commander, it's deathly quiet. Life check spells show there is nothing alive on this side of the city, and huge numbers of those creatures on the other" Firepot reported as they moved towards a sewer drain "Wait... Holy horseapples! There's thousands of signatures!"
"Sir, what the hay are those?" One of the Rangers pointed at a mass of beetles that were rushing through the drain towards them. They swarmed over the Equestrians, and, despite the Ranger's frantic efforts to get them off, filled every opening. One by one, the Rangers collapsed. Even Ossyan succumbed to the beetles, collapsing in a heap.
That was when Lord Commander Ossyan's life changed forever. It is unknown how he survived the insects, only a note found by an Equestrian Army Medic held any information. The beetles are how the Chimera spread their virus, the insects swarming into every orifice and causing the victims to go into a comatose state. None have ever woken up. Save Ossyan. It is unknown if the virus mutated in his system, or if he has a natural resistance to it.