Please check the following six possible causes if you cannot use a Duo or Harmonized skill.
2. You have a skill with a style equipped.
5. It is an event in which Duo and Harmonized skills cannot be used.
6. A Duo's Hindrance defensive structure has been placed in Aether Raids.
1. Smart End is on.
If you have Smart End on, the turn will end when all your units have completed their actions even if you could use a Duo or Harmonized skill.
Please check your Settings by following the below steps.
■ Steps
Tap Settings, then Smart End
Off: Even if all of your units' actions have ended, the turn won't end unless you tap End Turn.
On: When all of your units' actions have ended, the turn will end.
Excl. Pair/Duo: Even if all of your units' actions end, if you can switch which paired ally is in the lead, or an ally can activate a Duo or Harmonized Skill, the turn will not end.
2. You have a skill with a style equipped.
You cannot use Duo or Harmonized skills when you have a skill with a style equipped.
Example 1: Lyn: Of Blazing is engaged with the Hero in question.
Example 2: Celica: Sunlit Priestesses has a weapon skill that includes a style equipped.
3. You haven't met the requirements for use as explained in the Duo or Harmonized skill's explanation.
There are some Duo and Harmonized skills that can only be activated when certain conditions are met. Please check the skill explanation.
Example: Can only be activated if the Hero has entered combat during the current turn.
4. Your Hero is paired up.
You cannot use Duo or Harmonized skills while paired up.
5. It is an event in which Duo and Harmonized skills cannot be used.
Duo and Harmonized skills cannot be used in Seer's Snare or Your Time to Shine.
They can be used in Binding Worlds when the Hero is level 40 or higher.
Please check the Help and notifications for each event for information about maps or events in which they cannot be used.
6. A Duo's Hindrance defensive structure has been placed in Aether Raids.
There are times in Aether Raids if your opponent has a Duo's Hindrance defensive structure when Duo and Harmonized skills cannot be used due to its effect.
Read the Duo's Hindrance structure's explanation for details on its conditions.