Deathleaper

Deathleaper is a Lictor of Hive Fleet Leviathan, a hunter-beast the hive mind refined until assassination became a personality. It does not fight armies. It unmakes the people who make armies work, one terror-kill at a time, and leaves the rest of the city to imagine the next one.

Saint Caspalen's clergy learned that first. Other warzones learned it after. A Lictor is already a scout. Deathleaper is the scout the Munitorum writes about in the present tense because the past tense never sticks.

The hive mind does not need heroes. It needed a specialist that could panic a world before the first wave landed. It needed this.