Rifts are the origins of Entropy and determine where Entropy will spawn.
While two Rifts spawn around the Great Portal at the start of the game, it soon fizzles out after spreading enough Entropy . However, this won't be the only instance you will see Rifts in the game.
There's a method "combating" Rifts in MoteMancer. Note that this is different from combating against Entropy. You can combat Rifts without harming Entropy while also doing the reverse.
The method is through Incineration Spires and Downpour Bastions . The Incineration Spire focuses on sealing the Rift without affecting the nearby Entropy, though an upgrade later allows nearby Entropy to be cleared upon fully sealing a Rift. The Downpour Bastion focuses more on clearing Entropy, though an upgrade does allow it to eventually seal Rifts.
Since Rifts and Entropy exist on all six planes at once, this also means that clearing Rifts and Entropy will also cleanse them from all six planes simultaneously, too.
Upon clearing Entropy and sealing Rifts, you gain Entropy-related research points, which unlocks various Entropy-related upgrades.
When a rift is freshly formed, after a random period within the Spread Time range, it spawns three Entropy tiles adjacent to existing ones around it. It will only spawn up to its Minimum Range from tiles the rift itself is touching. If the Rift is not sealed, this range limit increases by 1 every 60 minutes up to its Maximum Range .
Once you do successfully seal a rift, the Respawn Time marks how long you have before the rift returns, as long as you are still harvesting from the mote field that formed it.
As you enter new planes, the Rift Tier increases for all rifts globally. When you enter your second plane (the Water Plane or Earth Plane ) you will start seeing Tier 1 rifts, and by the time you have visited them all they will all have become Tier 4 rifts.