The grey wolf that appears throughout the movie is a symbolic representation of Cloud's guilt. This has been confirmed by the writers. The wolf appears at the church, the Forgotten City, and Zack's grave. Cloud didn't show guilt at Zack death during the game because Cloud didn't have a complete mind when Zack died. It was hours, or maybe days, before he was a fully conscious individual again. During AC, Cloud comes to forgive himself for what happened in the past; Aerith and Zack are a part of that. While Aerith's not in the photo at the end, there's a bunch of flowers on the desk next to it, which could be interpreted as a reference to her.




