Place it at the end of a waiting scene as the payoff line, after the setup has made the delay clear. Open the moment with Law and Order Dun Dun for a dramatic beat, then let this clip answer, and follow it with SpongeBob Sad Song when the promised day never arrives.
このサウンドについて
This is a 5-second Spanish voice clip in which a voice repeats the phrase 'algún día', meaning 'someday', stretching the promise out instead of letting it settle. The repetition gives it a wistful, teasing feel, as if the day being talked about keeps slipping further away.