Effect:

"Soul Drinker" "Absorbs the souls of slain foes, growing stronger."

As you slay foes it will grow stronger and stronger. Each tier enhances all the stats and abilities of the sword. If you die without holding #33 Anubis's Mercy you will lose 1/2 of the stored souls (and a ghostly noise will play when you die.) It should note the amount of stored souls on the sword itself.

Tier 0 (Start)
6 Dam
1.6 Spd
0.625 Rec

Tier 1 (50 enemies slain)
7 Dam
1.7 Spd
0.625 Rec

Tier 2 (150 enemies slain)
8 Dam
1.8 Spd
0.7 Rec

Tier 3 (500 enemies slain)
10 Dam
2 Spd
0.8 Rec
Effect changes to "Soul Unraveler" "When fully charged deals extra damage to Living foes." (The bonus damage is basically 50% more.)
Also constantly drips dark purple droplets at this tier.