Who is Kostas and Daphne Mitsialis from Fugitive Pieces and what is their importance?

Kostas is a professor in Athens who shared an office with Athanasios Roussos before WWII. After the war, Kostas and wife Daphne host Athos and Jakob Beer during a visit from Zakynthos, taking them to a café where Vito the cook's singing once inspired Kostas to propose marriage. Jakob, at thirteen, is self-conscious and shy. The Misialis, however, provide him with clothes, get him his first haircut, and feed him. A victim of the Holocaust, Jakob is amazed by their kindness. Daphne seems like an elderly girl, and she paints cubist cityscapes. Starved for conversation, the adults talk about contemporary political matters that Jakob does not understand, but he can picture Kostas's vivid, bitter descriptions of the Nazi occupation. After Athos and Jakob emigrate to Canada, Kostas keeps Jakob informed about events in Greece through 1970, at about which time he dies.