Tenshi no tamago (1985)

a young girl is the sole protector of a very precious, large egg. her lair is near a large, abandoned, decaying gothic city inhabited by restless shadows. a mysterious young man arrives one day, and eventually wins her trust. they converse sparsely about obscure philosophical and theological topics, and she shows him some astonishing fossils and works of historic and scientific art. the ending is a bit shocking, and very ambiguous, leaving many unanswered questions and tons of room for interpretation.