There were some posts on page 16/17 stating that there is a certain part for case 5 in which you need to use the microphone. The poster asked how to use the mic on Desmume -- which wasn't answered -- but another user posted a save state to bypass the mic event.
Anyways, if you want to use the mic function yourself but don't have a physical mic, you can follow these instructions that I found online. It takes less than a minute to set up and I tested it and can confirm it works.
....If you do not have a microphone connected to your computer you can use the DeSmuME emulator to simulate microphone input. Click "Config" from the DeSmuME Menu bar and select the "Microphone Settings" option. Click the radio button next to "Use Internal Noise Sample" or "Use rand() whitenoise" and then click "OK." Click "Config" and select "Hotkey Config" to map a button on your keyboard to the microphone function. When the game requires you to blow into the microphone, press the selected hotkey to simulate microphone input.
Anyways, if you want to use the mic function yourself but don't have a physical mic, you can follow these instructions that I found online. It takes less than a minute to set up and I tested it and can confirm it works.
....If you do not have a microphone connected to your computer you can use the DeSmuME emulator to simulate microphone input. Click "Config" from the DeSmuME Menu bar and select the "Microphone Settings" option. Click the radio button next to "Use Internal Noise Sample" or "Use rand() whitenoise" and then click "OK." Click "Config" and select "Hotkey Config" to map a button on your keyboard to the microphone function. When the game requires you to blow into the microphone, press the selected hotkey to simulate microphone input.