Aerith is a world with only one season, winter, and chose to close itself off to the fae on Athare, although it didn't go to the extreme of forcing the only fae that travelled there away. Instead it trapped them. This did, unsurprisingly, affect the way the races on this world lived their lives, because of the fae living with them.
In the original group of five there were three members of the Gold family and this means that there are many different forms of time magic used here, including time travel magic. Those with the ability to travel through time have strict rules to guide them, but that doesn't mean there aren't people who break these rules, so things can change without warning. Most are unaffected by these changes, because of the way the magic works on Aerith, but all the other time travellers are, and those with some sensitivity to time travel magic.
The people of Aerith don't travel much, so they have very little knowledge of the world that surrounds them, although it is possible for them to learn about it if they wish to.
Although Aerith cut itself off from the rest of the Web there are still doors that lead to Aerith and it's also possible for someone to create a door that leads that, but only if Aerith is happy to accept them.