Full list of all 56 Tales of Zestiria achievements. It takes around 100-120 hours to unlock all of the achievements in the base game on Windows.
The base game contains 50 achievements, and there is 1 DLC pack containing 6 achievements.
This is proof that you've equipped items that activate a Group Union bonus skill. Each basic skill group has a skill corresponding to each of the five elements. It doesn't matter where on your equipment you have the skills equipped; just equip all five skills in a group to form a Group Union!