So you can get this achievement and also
Bond of Friendship
and
Support Skill Master all at the same time
I got this achievement when I was about 51-52. All I had to do was go into each one of my Support Characters and assign as much SP as I could to each of them, with as many characters as there are by that level they each should have about 50SP+ to spend. Just assign as much SP as you can and once you back out all 3 achievements will pop