Arth | Final Fantasy XIII - Lightning vs. Long Gui (no TP/shrouds) @arthogonal | Uploaded August 2010 | Updated October 2024, 9 hours ago.
I'm not sure the final Army of One was necessary, but better safe than sorry. This strategy is easier to pull off than Hope's, but took me much longer to come up with.

Lightning: T3 Edged Carbine
Snow: T3 Feymark
Fang: T3 Shamanic Spear

SYN/MED/SYN
SEN/SEN/SEN
SAB/RAV/RAV
RAV/COM/SAB
COM/COM/COM x2

Dr. Lightning in the house? The Doctor's Code is an emergency accessory in case you need to heal post-collapse. Thus, you can do this without cutting it as close if you give her a fourth Magistral Crest.

Update:
Check out my refined approach to this fight at youtube.com/watch?v=jpzfgj_x4-Q