Today a new patch came out. Patch notes here[www.konami.jp]

"It's now possible to add players you want to support directly from your friends list."

So yeah, they now gave us the chance to do this. This is the point of this whole group, but a lot of people have already played the game through and are no longer in need of protection.

This update came way too late, but if there are still people actively playing the game you can now do what you joined this group for, finding people to defend you or for you to defend.