What's that prestige class that ...

[Darkcouch]

I'm remembering a prestige class that lets you act as if you have various weapon enhancements, but it's not kensai or soulbow.  I think it was replacement for if you already had a feat or ability prior to obtaining that particular level of the prestige class, but I may be misremembering that part. I think it was a stealthy type character.  I've double searched all my reference books and 

[Stratovarius]

Shadow blade from Tome of Magic Shadow casting?

[Ithamar]

There is an illumian PrC from Races of Destiny, Shadow Sentinel I think, that lets you enhance a sword made of darkness.  Is that what you're thinking of?

And one from Magic of Incarnum as well that lets you do something similar as I recall.

[Darkcouch]

Shadow Sentinel might have been what I was thinking of, but I thought it was more than just the bane or keen.  Oh well.

[TC X0 Lt 0X]

Probably not this, but Soulbound Weapon Psychic Warrior can put enchants on its called weapon as an augment.

[Darkcouch]

The Imbue natural weapon feature of the Thayan Gladiator was what I was thinking of.