Once the mode is unlocked, you will start with a party that includes the Evoker.
Transcending an Evoker will give a wonder that permanently gives you the sub aura of their Arcarum summon. Nier and Geisenborger’s wonder will also grant HP.
Evoking Solomonis is scheduled for late July, and will be tied to Evoker transcendence.
You must be at least Rank 101 with the skill 4 of either Maria Theresa or Caim unlocked. You will then see a new Fate Episode that unlocks the mode.