Thread:KodachiZero/@comment-27144555-20151117090846/@comment-3215051-20151117102254

Basically, the chain system (or Kizuna, most people like calling it that but I don't.) allows you to have allies be "equipped" to other allies, resulting in the one it's being equipped to getting another ability that depends on the ally being used. There's apparently a bonus for matching classes (Soldier, Knight, Wizard, Cleric, Archer), and for matching jobs (Magician, Paladin, Guardian, Priest). [Zero]