Long before, when the sky was more lively, Theia roamed around to eat and move as it intended. It aggravated planets and stars. Despite numerous attempts, all failed to stop her. Theia only grew stronger, gaining more and more momentum.
One day Theia came upon Earth. Earth was a mere rocky planet, so Theia intended to run over her just like it did with others.
At the moment of collision Earth stole its eyes: one she turned into its vessel and one into a moon of the night.
Theia was a very desire-driven planet. She refused to obey any stars, nor did she want the inertial force to take over her life. She caused several calamities and was seen as a pain to many stars, planets, asteroids, organisms, and even atoms.
One day, when she was passing by the solar system, Earth, a great magician, lured her into thinking she is a weak planet. Theia was fooled, and the Earth stole her magic and sealed her into a moon. With extra, even excessive, amount of magic Earth was now rich with whimsical creatures. Theia tries to reach for her magic again from the moon every 15 cycles, causing seatide to rise, but fails everytime. This is the reason why magicians can't work consistently throughout the month. And also the reason why they are different from witches, who use magis from distant stars.