The following interpretations of 'metaphysical guilt', don't explain how 'metaphysical' in 'metaphysical guilt' connects with the meaning of 'metaphysics' as the fundamental nature of reality.
Source: Understanding Evil: An Interdisciplinary Approach, edited by Margaret Sönser Breen. p. 112 Middle
Responsibility under these circumstances seems initially to fall within Jaspers' category of metaphysical guilt: the guilt we all share in allowing bad things to happen, in failing to help others, in taking actions that may harm others in some way, and in continuing with our ordinary lives when we know that too many others are utterly miserable and that sometimes their misery supports our own lives.23
Source: Nahshon Perez. Freedom from Past Injustices. p. 94 Middle
Karl Jaspers, in his short essay, suggested distinguishing between four concepts of guilt: criminal guilt, political guilt, moral guilt, and metaphysical guilt.95 Jaspers briefly summarizes the four concepts as follows: [...] Lastly, metaphysical guilt is connected to one's status as a human being, which connects her or him to all other human beings. This connection makes him or her "co-responsible for every wrong and every injustice in the world, especially for crimes committed in his presence or with his knowledge.96 The relevant judgment of this guilt is with God alone. Note that Jaspers here emphasizes "human being" (rather than a citizen or a member of a specific community), and " God," as the judge, a notion which is inten- tionally far removed from individuals judging each other.
Source: Christopher J. Thornhill. Karl Jaspers: Politics and Metaphysics. p. 176 Top
It can thus be seen that Jaspers' concept of metaphysical guilt is closely related to his transcendent(al) interpretation of cultural and political traditions. Metaphysical guilt, he argues, is a guilt which results from actions which negate the transcendent(al) (metaphysical) qualities which inhere in human tradition — in this instance, the tradition of German culture. All Germans are guilty, Jaspers explains, because all Germans are the inheritors of German culture and this culture has been betrayed by the millionfold murder of Jewish people. The meta- physical guilt of Germans, however, derives only secondarily from the actual concrete fact of genocide: it arises primarily from the fact that the transcenden- tally human possibilities of the German tradition have been catastrophically by German people.34 Humanity (here, the humanity of Germans) becomes metaphysically guilty, therefore, wherever it wilfully refuses to recognize and be guided by the transcendent(al) ideas to which it has access in its (German) traditions and cultural forms.