Bombshell
After Linjos delivered both the magically sealed dimensional box and the coded letter, Lith felt like a burden had been lifted from his chest. It was the biggest, yet just one among many.
Now he had to prepare for the next dimensional magic exercise, research the runes sealing the boxes hidden inside his pocket dimension with the library's help, study their pseudo core with Invigoration, and find the time to use Accumulation to keep refining his core.
Now that he had finally overcame the bottleneck, he could use his first breathing technique again, to amass the world energy and strive for the blue mana core.
Worst case scenario, it would make him as powerful as the Headmaster or a Professor. Lith had not missed how the more he refined his core, the more dramatic changes he experienced.