Slight variation on the Death Cult Assassin:

Starting items: Replace x2 Best Quality powerswords with:

x2 Crimson Grace:

1d10 + 7 Pen 3 Damage type: R

Qualities: Lathe, Balanced, Toxic (25 doses), Nerve Render

Nerve Render: Upon being struck, the enemy must make a toughness test or suffer 1 point of fatigue. This toughness test begins at -0 with 0 damage, and -5 difficulty per damage dealt. Every 2 degrees of failure adds another level of fatigue.

And also allow the taking of the Berzerker Paragon Talent. Forgot to mention that.

That seems like a lot of damage for a non-power weapon to be doing. It doesn't sound like it even has a chain edge.

I like how it is both toxic and also gets a super special effect to make it do extra special damage. At this point, why not add force, sanctified and powerfield?

To be serious, look at the newer DH/40k RPG books for special rules/inspiration if you must. Razor Sharp would be a good choice, fluff it as something like "Only in the hand of a Moritat, who are trained in the perfect art of the cut, can this blade rend straight through armor that would stop lesser bladewielders with ease"

Sanctified might be a neat bonus, *shrugs* but as is, it doesn't look good

How about you get a pair of neuro gauntlets instead? Fluff them as swords or daggers if you like.