The Shadow Nexus (mission)

Challenge Mission. This is a 4-person challenge mission. The goal is to close the Torment Rifts before a hole is torn in the dimensional fabric. This is done by killing the Margonite Portal Mages that guard each rift. As long as a rift stays open, the rift progress bar will continue to fill (one tick per open rift). Once it is full, the mission will end.

Initially, each portal mage will be guarded by 2 enemies. As the mission progresses, more enemies will accompany them, making subsequent battles more difficult. You receive 10 points for killing portal mages and 1 point for all other enemies.

Rewards
Mysterious Armor Pieces are awarded randomly [when Portal Mages are killed?] which can be used to change the skin of armors for Zenmai, Olias, Norgu, Goren or General Morgahn.

Tactics

 * The "U" map shows the location of all the potential rifts with gray flags (similar to the Alliance Battle map). An open rift shows as a red flag.  Use this to optimize your paths to the next open rift.
 * Like most challenge missions, speed buffs are very important to get to the next rift quickly.
 * The portal mages are not only in charge of the rifts, but they are also powerful elementalists, so it's important to kill them as quickly as possible. Although the other creatures around the rift don't have to be killed, they will remain and make it harder the next time a rift opens at that location.

Travia

 * Nexus probably refers to a secret (fictional society, which first appear in Ravem's Gate, which is one of five books written by Anthony Horowitz and which bring the name of The Power of Five.