Shibumi (1979) - Trevanian

Nicholai Hel, born in the ravages of World War I China to an aristocratic Russian mother and a mysterious German father, raised in the spiritual gardens of a Japanese Go Master, survives the destruction of Hiroshima to emerge as the world’s most artful lover and its most accomplished and highly paid assassin. Genius, mystic, master of language and culture, Hel’s secret is his determination to attain a rare kind of personal excellence, a state of effortless perfection: shibumi.