Virgil - Febronia

Obviously, Febronia is a very integral part of piecing together Virgil's past and motives. Febronia is a Transgenic type model of Realian, and is, in fact, half-human; the only reason why Virgil could take her transplanted organs into his body was because of the way her body was constructed.

Febronia was everything a Realian wasn't, in Virgil's eyes. She was kind, selfless, loving, and understanding. This seriously confused him, as he was taught that Realians were nothing more than killing machines you had to kill before you or your comrades were killed by them. It's similar to how during the Chinese Holocaust (The Rape of Nanking) the Japanese soldiers were taught to view the Chinese as less than human.

It may have seemed that Virgil's views were about to change. However, seeing the person he has come to show affection towards died right in front of him seemed to have caused him to regress even further; he ended up eating Realian neuro-parts in order to find out the remote self-destruct code, and treats Realians as manufactured objects. He doesn't hesitate a single moment when he sets the Realians aflame aboard the Woglinde.

However, it's still clear that Febronia made an impact on him, even if it wasn't one she wished for. He calls out her name when he dies, and most likely even became a Testament in order to fulfill a wish. Most of the Testaments became so because they wished for the Eternal Recurrence to occur, to relive that one moment in their life where they could be with the one(s) they were the most happy with. For Albedo, it was to be with his brothers. For Voyager, it was to be with someone who cared for him (presumable Jan Sauer and the rest of the squad, up to interpretation). For Kevin, it was his mother (and possibly Shion). For Virgil, Feb is a likely candidate.

Still, finally, the two got the happy ending they deserved, and were able to talk before disappearing together, a la Shuyin and Lenne in Final Fantasy X-2.