Hm...this is a more general idea on the Raid Tier, but with all of the talks of FFXIV's themes recently, Nier is actually a pretty good choice! Spoilers for Nier, Nier Automata, and FFXIV below!
Consider playing them before spoiling yourself. They are highly recommended!
One of the primary themes of FFXIV so far is the idea that one has to give up the past and push for a better future. Those who are able to move on tend to build better happier lives/societies, and those who can't tend to end up as villains. The Garlean Empire can't forgive the other nations for their mistreatment ages ago. Yotsuyu cannot forgive Doman Society for mistreating her. Vauthry can't give up on his self-indulgent paradise despite it harming others and doing tons of long term damage. The Ascians are ready and willing to eliminate entire worlds to reclaim their home.
In the Nier series (it's slightly less prelavent in Drakenguard but who cares since we're talking about Nier) many of the characters including the protagonists are trapped in similar self-destructive cycles. They fight for a world that was, desperate to reclaim without really understanding what made it great.
In Nier, both the Gestalt and Replicant versions of Nier cannot cope with the coming death of their daughter (or sister but I played Gestalt), Yonah. Yonah herself accepts her death and simply wants to spend more time with her father. But neither of the fathers seem to care about her wishes, instead plunging into destructive quests to save her. The Gestalt begins a war between Shades and humans and attempts to steal her body to save Yonah (not unlike several plot points in FFXIV). The Replicant spends the rest of his life on a mad crusade and eventually dooms all of humanity to extinction.
In Nier Automata both the characters and the entire setting are stuck in dangerous cycles of revenge, violence and misery. The Androids and Machine Lifeforms eternally battle for masters that have long since disappeared. Neither side can truly move on, despite desperate attempts to. On the individual level the game confronts characters stuck in ruts seeking their own absolution, whether through revenge, destruction, or impotent rage. These sorts of characters fit well into FFXIV as it turns out.