The description for this trophy is a bit misleading. Either that or the trophy is simply glitchy. I managed to unlock it after I used every COMBINATION of disciples for at least one mission. So if you have used each one at least once and don't have this trophy, try noting down each combinations you use. There's only 4 disciples so it's not that many different combinations. Also, the only time I ever used just one disciple was when I only unlocked Dito, so don't worry about using Decadus, Octa, and Cent singularly. If you still don't get it after using every combination, then that must mean this trophy is glitchy and you should get it to pop eventually.