Place it at the reaction cut itself, not over the build-up, then follow with the Anime Wow Sound Effect for a bigger second beat. For a flop moment, swap that follow-up for a fail sting instead, keeping this ahh as the first response in the sequence.
關於此聲音
This is a very short, high-pitched anime-style ahh, under a second long, delivered with a soft breathy release. It reads as surprise, relief or a sudden realization in one quick beat. The feeling is light, cute and playfully dramatic, making an ordinary reaction sound startled and more animated without any dialogue needed.