Episode 3: Magus and Alchemist

Before all of the students in the academy went to the southern island, it's shown that Yui saved Arata from certain death by dragging him into her dream world. She then proceeds to tell him about magic and the seven archives of magic. She also explained he might able to control his powers by choosing his thema, which is founded in either of the archives. He then proceeds to stop the Breakdown Phenomenon after being released by Yui and choosing his thema. The magic that stopped the Breakdown Phenomenon also caused all the people around him, except Mira, who reflected his magic, to have their clothes dispelled and destroyed. On the island, he showed Serina his new-found magic prowess, breaking her swimsuit in the process. In the hot springs, Arata requested that Lilith demonstrate her magic. She reluctantly accepts it after Arata's constant pleading. After witnessing her spell, Arata requests the grimoire to copy the spell for him, which works out successfully, surprising the entire group.