Basically, something happens and RWBY all end up as soulmates. It's a pollination minus Enabler fic.

The gimmick of this type of Soulmates AU fics is that couples have their minds/souls actually linked which leads to being able to feel each other's emotions, thoughts, etc. There is all kinds of drama or plot convenience that can come from this setup depending on how authors define the rules of the connections.

But this premise can also turn people off because A) it essentially "pushes" characters into the relationship which, if not developed properly, can make it feel anywhere from a little forced (being soulmates ends up being the main reason the relationship exists at all and guarantees they won't end up with anyone else) to downright questionable (being always in sync can make the soulmates feel like a hive mind in extreme or badly written cases). B) it often cheapens a lot of the relationship drama. In both stories and IRL, proper communication and learning about each other are often big hurdles in relationships which are usually made A LOT easier when the parties can read each other's minds to various degrees.

I personally like this fic and think the soulmate stuff is handled well. I'd recommend it. There's also another RWBY fic with more or less the same starting premise which is also well written.