After being Reincarnated as a Cat Girl, I Somehow obtained a Unique Subclass

the Grand Sage's Floating Sanctuary Part I

At the guild, the prince approached the counter and she overheard him discussing dissolving his party. The receptionist waved Zatiel over and informed her that her party's ranking had passed novice and raised to full-fledged from the reclaiming of the mythril mine. The prince's party was nearly qualified for full-fledged ranking as well; so the receptionist offered that there would be no issues in combining the parties, but asked her to return with an updated status sheet soon.

Once the paperwork was finalized, Zatiel led them to the magic circle, and instructed them, “Just stand on the magic circle and say The Sanctuary.”
They all moved onto the circle with her and she led them in saying, “The sanctuary.”

The magic activated and her party was soon surrounded by books. She also noticed the spirit returned. Without warning the spirit cheerfully greeted her.

“Why hello, Mistress. It would seem these are your trusted companions?”

“Yes, of course. Can you tell me ways this place can make us stronger?”

The group watched her with both anticipation and confusion, but the spirit answered directly, “Why certainly. One sure fire way to make a group of warriors stronger in the fastest way possible would be to introduce them to one of the several copies of Book of the Grand Sage. I even suggest you read it as well, it will fully explain much about this world and how world magic works. For your friends, this will result in a subclass evolution to some type of sage depending on what they choose to do with the information in the book and their individual aptitudes. The bookshelf closest to the desk is full of them.”

Zatiel walked to the bookshelf and started placing books from it on the desk, one for each of them as she spoke, “The spirit says you get a subclass evolution if you read this book. We can visit the armory and investigate the town, after we read this and use the artifact to upgrade classes.”

The group gathered around the table and opened the books. Each began to read at their own pace. Claire stood closeby to Vanessa to help her, while the prince settled in with the copy next to her own. The readers quickly became absorbed with the task.

The book itself started with several lines of runes that cast spells and went on to explain that skills and magic schools were world magic written into existence by the gods themselves. That the skills and schools only measure and govern the abilities of this world, most skills could be gained. It went on to describe other world magic written by the gods such as the laws of physics, magic, and dungeons.

Dungeons are created and maintained by the Goddess of Chaos to create places for mortals to gain valuable resources and grow stronger by facing adversity. The book took a twist and started explaining certain individual skills in detail, mainly skills and spells to improve memory. In many cases the book's explanations ended with a line of runes that cast a spell once read.
It went on to explain that any person with mana could, with enough effort, learn the basic spell of any school of magic. The only limitation was darkness and light magic, with access to one the other is restricted. All physical and mental skills were obtainable through dedication of the basics, though having a natural talent for such things makes it easier.

The book went on to give a basic summary of the schools of magic along with the most basic spell for each school. With a little effort, she was able to produce results with each spell. Though, the spells for the schools she had studied were all new to her. Like the basic spell absorb light, a darkness spell that weakened light sources surrounding the caster.

Like the book suggested, she made no progress with light affinity magic. Several other schools of magic were explained, like spirit magic, runic magic, and summoning magic. The book continued to unravel the secrets of the world, also explaining classes along with unique awakening subclasses like the sage, demon lord, and hero series of unique subclasses. The book went on to explain that a proper appraisal can reveal a lot about anyone's latent potential.