The preparation took one week to complete. That was due to how many things Theo needed to finish before the trip that would last for three months.
Due to his target this time, his goal was to reach Level 680 to 690 on this trip alone. Hence, with another two short trips, he should be able to become a Mythical Rank Expert, thus fulfilling the promise with Agata.
Of course, fighting against a Mythical Rank Monster was easier said than done, considering Theo's current level only at 615. There was a huge gap in their level.
So, Theo only aimed for Normal Class monsters which shouldn't be that powerful. He would avoid Rare Class and even General Class Monsters since they would be too dangerous to fight.
To defeat a Mythical Rank Monster, Theo made a huge change in his skill set, especially to his Illusion Destruction, Magic Augmentation, and Magic Power Expansion which felt quite lacking in the past few months.