Frontier Rift is a Global Exclusive harder version of Frontier Gate.
It is a gauntlet of battles that rewards you based on certain goals you need to hit.
Some rifts are also required to have Omni plus units to enter.
From Forgotten Magic onwards, the content targets guild cooperation on thresholds for unique rewards.
Essence of Time
Joys to Ashes
There usually a Guild Featuring a Rift. The Guild must all contribute their score to reach milestone rewards.
Rewards from Guild Tokens to Rift Tokens are rewarded after the Calculation Period.
On August 2018, the game started to re-run Frontier Rift, introducing a Memorial bazaar with memorial tokens from Guild score threshold to exchange for the unique sphere or/and unit.