Vergänglichkeit translates to "transience" or "ephemerality". It's a profound and somewhat poetic word that refers to the quality of being temporary or short-lived.
In the song, Bernhard Brink sings, "Wir fühlen uns von Vergänglichkeit befreit" (We feel ourselves freed from transience). This word is particularly interesting because it captures the central theme of eternal love and timelessness that the song celebrates, making it stand out from more common vocabulary.
Bernhard Brink turns a couple into something that won't wear down. The dusk settling in ("Die Dämmerung geht schlafen" — "The twilight goes to sleep") sets a quiet scene before the hook lands: "Wir sind zwei Diamanten" ("We are two diamonds"), a love that's "ewig und unendlich, wie die Zeit" ("eternal and infinite, like time"). The images keep building on that idea — faces "in die Seele graviert" ("engraved into the soul"), light breaking "in meinem Herz in tausend Farben" ("in my heart into a thousand colors") — all pointing at two people who, like diamonds, don't fade the way ordinary things do.