"Myra, did you ever read or know something about mana?"
They can't defeat the boss without the help of mana power, so she informed the girl in advance.
Before there was Time, the Sun, indeed all the Stars, billowed forth not only light and heat, they blew forth that which Men now call "Magic" or "Mana" in this game world.
It was a component of Star Breath, which Men also much later began to call the "Solar Wind." When Time began, the Stars ceased to breathe Magic, for Magic was Timeless and once Time began to rule the Universe, Magick was no more created. It had to be hoarded and the supply slowly dwindled.
It serves as a life force and even contains the essence of the soul. Every person is born with varying amounts of mana but through various means have the ability to gain more whether by training or taking it from elsewhere like from other people, monsters or gems.