The return trip was much faster for Isaac than the journey out, thanks to Space Teleportation.
Therefore, by the time Isaac returned to the Underground Palace City, the materials for the Ten Divine Books had yet to be fully collected. Only a small portion had been gathered, so progress was not ideal. Fortunately, Isaac hadn't spent his entire trip just conducting experiments. He had also visited the three major Magic Cities and some of the smaller ones nearby to open a line of communication. Going forward, he could purchase some of the materials directly from them.
Of course, for now, he could only trade with the nearby Magic Cities. The three major ones were quite far, and establishing formal trade routes involved some troublesome procedures. First, a Teleportation Array had to be prepared. Second, aside from the Arcane Capital, the other two had been built by Legendary Mages, so he first had to find a way to negate the influence of their Mysterious Attribute.
