Guilt. The heaviest burden.
An old man has for many years borne a weight that runs deeper than survivor's guilt. He is a survivor, of humanity's darkest hour, but wouldn't have lived through it if not for the actions of another.
Now he has the opportunity for which he has long yearned: to meet his saviour's daughter and tell her about her father's supreme act of selflessness. And maybe, in the telling, one of them will find release.