I knew I should've waited a while before handing out hints. shinangel2292, you're correct; it was Lucrecia.
Akin to the aerial cataclysm (Sephiroth believe Jenova (the calamity from the skies) is his mother, when in fact Lucrecia is his mother)
Sided with the adversary (Lucrecia chose to be with Hojo instead of Vincent)
Despair and penance (Vincent punished himself for not protecting Lucrecia from Hojo)
The escort does writhe within. (More of the above)
