[Folket]

I would say that Charm, Thaumaturgi 7 is your best bet.

A N3 oreiad have 18% chance to charm a Niefel giant. With eye of the void (5 astral pearls) it is increased to 30%.

For the cost of fielding 30 niefel giants and a niefel jarl you should be able to field 10 oreiads with eyes of the void.

Just put the mages close to the enemy with chaff with hold and attack orders in front, so that they are within your 20 range.

With three giants deserting every turn you should be able to win the battle.

Your average Oreiad should be able to cast charm 5 times before passing out. Those with nature random should be able to cast it 9 times.

You can also forge rune smashers and spell focus with your mystics. With spell focus, rune smasher and eye of the void your Oreiads will charm 54% of the time.

I think your second best shot is living clouds and lightning.
With storm and storm power your Oreaiads with air random should be able to cast living clouds twice. On average it will take the niefel giant 13 attacks to kill an air elemental. Slightly less if the elemtal is attack several time a round. So if you manage to summon 30 air elemental, the giants will be stuck for a while. The air elementals will do AN damage and will not be hurt by lightning spells you cast. Air elementals will also work well as chaff if you are casting charm.

You can give a crystal matrix to an Oreiad with air random. Use her with 8 mystics casting communion slave. After storm power each casting of living clouds will give you 7 air elementals. Theoretically you should be able to cast living clouds 8 times before your communion is to tired. But the AI will probably burn to many gems for that to happen. On the other hand if the AI burn more gems then needed you will get 8 elementals.