Here is the full list of all 15 Defenders Guild achievements.
Add a debuff to an enemy.
Add 4 or more debuffs to an enemy.
Turn on any indicators.
Open the info menu of any enemy.
Complete a mission using less than 4 adventurers.
Complete a mission using just one type of adventurer.
Use the targeting sistem.
Upgrade a character.
Complete all the Aerias Field quests.
Complete all the Frost Mountains quests.
Complete all the North Desert quests.
Complete all the Death Fields quests.
Complete all the Fire Forest quests.
Complete all the Eastern Islands quests.
Complete all the Dreamlands quests.