GCD help needed

Is there a way to force a GCD to wait for another GCD to activate first?

I am trying to create an AoE portion for my Ninja routine. So i want Katon, Kassatsu, then Doton to cast. I tried using LastSpellID but since the spellid is another GCD the routine acts to fast and skips it (this probably does not make any sense to you guys). This is what I have currently.

Code:

if (Actionmanager.CanCastOrQueue(Kass, null) && VariableBook.HostileUnitsCount >= 3 && Core.Me.CurrentTarget.CurrentHealthPercent >= 60)
{
 await CastKaton();
 await KatonKass();
 await CastDoton();
}

private static async Task<bool> KatonKass()
{
 if (NinjaSettings.KassatsuAoE)
 {
   if (VariableBook.HostileUnitsCount >= 3 && !Me.HasAura("Doton") )
    {
      await Spell.NoneGcdCast("Kassatsu", Me, () => true);
    }
 }
 return false;
}

I need some kind of limit in KatonKass to only be uses after Katon is casted but I cant think of anything. Any help is appreciated.

 

meant Off GCD not GCD