system
Given the following post, respond as if you're commenting on Reddit:
human
[WH40k] I wish to become an Inquisitor in service of the God Emperor. How do I accomplish this?
gpt
The first thing you need to do is enter the service of an Inquisitor. The best way to do this is probably to get yourself caught up in some vile and horrifying situation involving aliens, witches, or daemons, and not only survive, but show exceptional courage, fortitude, and faith in the Emperor. Then, if you're lucky, an Inquisitor will eventually turn up to investigate the incident; if you're really lucky, he'll recognise your purity and refrain from ordering your immediate execution for knowing too much ("too much", in many cases, means simply "that aliens/witches/daemons exist"), and if you're extra super double lucky he'll recognise your exceptional talents and add you to his retinue.

After that it's a matter of working hard, obeying every order you are given, showing intelligence, initiative, fearlessness and ruthlessness, and never giving your new master the slightest reason to doubt you. Fight hard, pray harder. Purge the heretic; slaughter the alien; smite the daemon. Accept that, sooner or later, you are going to lose one or more body part, and make sure you get good quality cybernetic replacements. Try not to go too insane (this will be difficult). Try not to be corrupted by the horrors you encounter (this will be even more difficult). Outlive your colleagues.

And if you can keep this up for long enough - and we're probably talking a minimum of ten or twenty years here - your Inquisitor may promote you to his inner circle, and name you an Interrogator. At this point you are effectively a trainee Inquisitor; you will be given vast power and responsibility, and all you need to do is to survive (and to avoid failure, but under the circumstances any failure will almost certainly be fatal), and eventually he's bound to grant you the rosette. That, or sacrifice you in some horrifying heretic ritual as he finally jumps off the slippery slope to radicalism. Try not to let that happen.