Harakoni Warhawks
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 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 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 more stronger than what a normal Elysian force could use. However since Harakonis are in low numbers due to being stormtroopers, 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.
GW doesn't have many instances with them fighting much in the 41st millenium 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 dissapoint.