Fairies weren't supposed to go out of the boundary of the forest, but Vivi was spurred on by her curious mind to check out what the Rebornians were doing.
While in the mirror dimension of the Fairies, Vivi traversed outside the forest and went towards the Rebornians.
This allowed her to stealthily spy on these Reborn people without them knowing about it.
As she got closer, the first thing she noticed was the road they built beyond the horizon. Even she was impressed. It was incredibly flat and made out of sturdy natural materials. No magic was involved in it.
This made her all the more impressed about the people making them.
They all seem to be performing intricate and complex types of magic that she had never seen before. These spells were weirdly specific and seemed to be molded perfectly for their jobs.
For example, the ones in charge of digging used spells that specifically created a wide uniform path the same as the road behind them.