In the electronic application system operated by HARP Co., Ltd., when electronically applying from a smartphone, you can use the electronic certificate (signature electronic certificate) installed in your My Number Card to electronically sign the application form. This is an Android app for doing this.
This app is provided by HARP Co., Ltd.
https://www.e-harp.jp

Notes:
This app requires the installation of "JPKI User Client" to perform signature processing.
Please install and use the JPKI user client from the link below.
https://play.google.com/store/apps/details?id=jp.go.jpki.mobile.utility