"Hitler made only one big mistake when he built his Atlantic Wall. . .He forgot to put a roof on it"
- - Stephen E. Ambrose, Band of Brothers,(the book)
Take the Elysian Drop Troops, now add 50% more badass, now replace their normal lasguns with hellguns and their flak jackets with carapace armor, and now make them all
STORMTROOPERS (Sadly they aren't, along with the Elysians it was later revealed that their elite troops are not even their own soldiers, but Tempestus Scions sent to babysit the regiment, which kind of takes away from their overall badassness) and you have the Harakoni Warhawks, one of the most elite guard drop units in the galaxy.
All Warhawks hail from the Hive World of Harakon, where their massive Hive Worlds (Hive Cities?) have spires reaching into the upper atmosphere due to the world having a much lower gravity threshold. In order to hunt on their homeworld they use grav-gliders to hunt in the valleys below, this makes them excellent at high altitude jumps as well as judging air currents on the way down. The Harakonis are very distinctive with their uniforms and many a guardsmen can tell if a guardsman hails from Harakon just from their distinctive dialect of Low-Gothic. Many Imperial Commanders owe thanks to Harakonis attached to their regiments, because their punch is much stronger than what a normal Elysian force could use. However since Harakonis are in low numbers due to being stormtroopers (so basically Imperium's special forces), they need to be at the right spot at the right time to make a difference, but if they are, oh man, they will fuck shit up.
Unlike Elysians, Harakonis make full use of heavy weapons teams and Special weapon squads which allows them to pack a MUCH stronger punch. However since the Warhawks are a drop unit like the Elysians, they have no armored vehicles, this coupled with the fact that they operate in low numbers as heavy infantry means that they need support from other regiments in order for them to survive. Additionally, being armed with power-hungry hellguns and heavier weapons they run out of ammunition pretty quickly, and with their carapace armour they also tire quite fast and thus Harakonis cannot be used to capture and hold key objectives behind enemy lines (that's what Elysians are for, after all), and are pretty much limited to be dropped on the front line. GW doesn't have many instances with them fighting much in the 41st millennium for some reason. Basically when you absolutely, positively, need to GET SHIT DONE and require the kind of force that would be able to deal with threats such as heavy infantry, the Warhawks will not disappoint.
The Warhawks are now more easily represented than ever - whereas the Elysians are meant for airborne invasions, utilising their transportable-by-air vehicles and weaponry, the Warhawks are small and elite insertion teams brimming with special weapons and carapace armour. This makes them ideal candidates to be represented by the Tempus Militarum list. While they have no models, they can easily be made by splicing together some Cadian bits and greenstuff (as well as the grav-chutes from the Elysian line of Forgeworld, if money is something you pick out of your arse on your foreign planet). You can also use tempustus scions as a base, and add Anvil Industry PASGT with Gasmask heads, along with afore-mentioned elysian grav-chutes.
The name "Harakoni Warhawks" is a reference to the Dune universe. In the first books of the Dune Series the House Harkonnen acts as main antagonist to the House Atreides which uses the Hawk in his banner as (war) symbol. House Atreides was characterized for its use of air weaponry in some media.