Place it at the very end of a farewell scene, after the last line of dialogue, and follow it with Sad Violin to underline the departure. For another edit, put Anime Punch just before it so the goodbye closes the scene.
關於此聲音
This is a very short voice clip of Kasumi saying “sayonara,” lasting under a second and delivered in a clear, gentle tone. It feels light and wistful rather than dramatic, like a soft farewell that lands quickly and leaves a small smile. The single word carries the whole moment, making it easy to recognise and fun to drop when someone is heading out.