There are plenty of alternatives to the phrase "first occurrence." One option might be "initial appearance," referring to the first time something is seen or encountered. Another possible synonym could be "debut," highlighting the novelty of the event or object in question. "Maiden occurrence" or "debutante moment" captures the idea of something being born or introduced for the first time. Alternatively, "genesis" emphasizes the beginnings of something, marking the very first step in its journey. For more technical contexts, "origin point," "inception," or "primary event" might be useful replacements for "first occurrence".