NacaHelper is a small application that acts as a middleman between your ACom and your web browser in the case your web browser does not support using the Web Serial protocol. Currently it exists for Windows/Linux and Android.
Download it, open it and then choose the COM port corresponding to your ACom, then press on "Connect to serial". Once done, you can use your ACom from within NacaBattle by using the NacaHelper option. When done using, press "Quit" to close the app and close the serial ports.
In the case of Android, after installing the APK, open it and then connect your ACom to your phone. You will get a pop up asking for permission for the app to connect to your device. Once connected, the application will say so, then you can change back to NacaBattle and continue over there.
Once NacaHelper is running, the button for that option will pop out, allowing you to use it.
You can download a prebuilt version of NacaHelper from here.
Feel free to use in your projects and adapt as you wish.