Wow, sorry mate.... it might have been a mistake? Rest assured, I will never offer YOU any advice again...
I'm sure your post will either be ignored or blown out of proportion somehow.
Then the Inquisition shows up with reports of daemon worshipping being conducted somewhere on the planet. Anyways, the efforts to stop Chaos from taking root fail and so actual military action must be taken.
Daemon worshipping implies a cult, for which an inquisitor would have his/her retinue, any inquisitorial forces brought, local authorities, and the planets PDF. If all of this fails then that likely means the cult has received aid from their patron(s) and either specialists are needed (aka the Grey Knights) or the world is doomed.
The Imperium at large suppresses knowledge of daemons and chaos.
Battle-capable adults are drafted immediately into the Imperial Guard, including Faris, and he finds himself drawn into a war.
At best Faris and the other capable adults would be drafted into the planets planetary defense force, not the Imperial Guard.
Something I'm wanting to do with this short story is show a lot of character development in Faris. Starting out he is obviously a believer in the God-Emperor and the Imperium in general, but he does not feel like he owes his very life and finds it extremely unfair when he is drafted and separated from his family.
If Faris is someone who was taught to believe in the God-Emperor than he would be more than willing to put his life on the line if it meant protecting his family, likely hoping that the Emperor would protect him so that he could see and be with them again.
Most people view being drafted to fight in one of the Emperor's armies as an honour, yet another way to show his service.
Some examples I've already come up with include him fearing his first time going into battle, but being inspired when he meets a member of the Deathwatch.
If his world is struggling against the grip of a chaos cult intent on worshipping daemons then why would a marine of the ordo xenos be present? Deathwatch are alien hunters, not daemon hunters. Theres a chance a company or strike force of space marines would answer a call of aid from the inquisitor since he and the forces he initially had access to were not enough. With what your doing, the deathwatch have no business on the planet.
On the field of battle he witnesses horrors and heroics alike. He has a conversation with a Space Marine about family, love, and duty. At the end he is in a hopeless situation but has accepted that he is now a soldier, willing to risk his life for the Imperium like any good Guardsmen should be.
Most citizens of the Imperium are likely told that service to the God-Emperor and the possibility of sacrificing your life is the greatest show of faith. Faris would/should know this going in, and at the point your leading to come to understand and fully believe in it.
What do you guys think?
Short story or not, I think your trying to cram a few to many things in for the sake of having them.
One of the biggest issues I see is why an inquisitor would allow locals to fight against a cult now rooted in their own planet. Whats to stop some of the draftees from being cult members and sabatoging Imperial forces that they now have access to?
If it was a xenos cult, like genestealer, then draftees could be screened. That would also mean you could include a Deathwatch team.