Title: Shrapnel
Author: Lookinglass
Rating: M
Genre: AU
Pairing: Some Ulquihime.
Status: Complete
Summary: World War II: Grimmjaw is an exhausted U.S. soldier, dragging his platoon through dirt, dead bodies, and despair. Ulquiorra is a detached German officer, efficient, obedient, and ready to serve his country. A piece of shrapnel brings the two together.
Link: http://www.fanfiction.net/s/4068401/1/Shrapnel

Ignore the (mis)spelling of Grimmjow's name. Other characters from Bleach show up in this AU piece, but it's not as AU as you think, as later chapters reveal. In fact, this could be viewed as more of a mini-prequel. Warning: Torture gets rough. Also, no Ichigo.
In any case, I really enjoyed this story. Some good action and suspense, and a twist at the end that I liked a good deal. I'd give it a 5/5. No Bleach knowledge needed to enjoy this story, although the twist and the character parallels won't be as interesting.

 

Just checked it out and read it one sitting. Whoo! Perfect balance of angst and grittiness and love the dark humor.

I wasn't expecting that twist near the end either. Anyway, I snooped around the author's profile and he recently updated with a two-shot sidestory for Shrapnel on Ulquiorra.

So follow-up rec:

Title: Shards
Author: Lookinglass
Rating: T
Genre: AU
Pairing: Again very slight Ulquihime.
Status: On-going
Summary: In a broken mirror, Ulquiorra reflects on his past before he became a Nazi soldier. A companion piece to Shrapnel.
Link: http://www.fanfiction.net/s/5896686/1/Shards

Not my favorite character, but I love the guy's writing style and I'm still waiting for Grimmjow's chapter.