This article talks at length about Dragon Quest XI's endgame and post-game, so here's your very necessary spoiler warning!
About 30 hours into Dragon Quest XI's story, you reach the holy town of Arboria. Its pious citizens are familiar with the legend of the Luminary who'll deliver the world from darkness, so they're glad to see you. In fact, you set foot in Arboria just as its high priest is baptizing a baby under the boughs of the World Tree, Yggdrasil. When you talk to the newborn's parents, you learn they've been trying to start a family for years, and your timely arrival is surely a good omen.
Shortly after you climb Yggdrasil and attempt to retrieve the legendary Sword of Light necessary to bring down Mordegon, a story twist ushers the evil being directly into the holy land. Mordegon corrupts the very heart of existence, causing the World Tree to rot and twist. Darkness spills across the countryside. You're shunted far away from Yggdrasil and Arboria, but when you make your way back to the town—after travelling through cities and landscapes ravaged by monsters—you discover the baby whose baptism you witnessed is dead. He wasted away shortly after Mordegon seized Yggdrasil, leaving his heartbroken parents to mourn his passing amidst Arboria's rubble.
Anyone who's unfamiliar with Dragon Quest can be forgiven for not realizing the series isn't afraid to punch you in the gut. As a lifelong fan, it's something I often forget until the game I'm playing pulls a Final Fantasy VI on me and kills off the baby of a young, hopeful couple. Maybe I'm more used to melodrama from Final Fantasy games. Or maybe Akira Toriyama's imaginative monster designs just give off a gleeful aura that makes it easy to forget the fifth installment of this series forces its child protagonist to watch his father get beaten to death by monsters before he's sold into slavery. Either way, make no mistake: Dragon Quest goes hard.
Dragon Quest XI goes particularly hard; your travels give you a front-row seat to some rather bitter events. Among other happy goings-on, a mermaid commits suicide after learning her human lover is dead, a horrific curse befalls Erik's sister, and a warrior-turned-dragon eats his own mother when she sacrifices herself to stave off the endless hunger that causes the beast to turn his eyes towards innocent people.
Also, Veronica just straight-up dies. After the world ends, the Luminary needs to travel the world and collect his scattered companions one-by-one (that should sound familiar). When he finds Veronica, she's slumped, unresponsive, in a grove where she and her twin sister, Serena, used to play. It becomes clear she sacrificed herself to save everyone during Mordegon's assault on Yggdrasil. Serena tries to mute her devastation, but she's understandably incapable of hiding it.
Don't mistake Dragon Quest XI for a grim, hopeless game, though. The front-and-center positioning of the World Tree is a giveaway, but the Luminary's journey emphasizes hope and rebirth. Your home town, Cobblestone, becomes the last gathering of civilization in the Heliodor area after the World Tree dies, and everyone pulls together to build it up—even the remorseful Heliodorian soldiers who are ordered to raze the hamlet near the start of the adventure. Within the fortified walls of the Last Bastion, adults adopt orphaned children, soldiers fight off marauding monsters, and everyone holds it together until you're able to bring down the immediate threat sniffing just outside the fortress' walls. Once you do that, the people of the Last Bastion breathe a little easier.
Dragon Quest XI sends you from one besieged town to the next and asks you to prop up its populations as best you can before you go off to confront Mordegon. The story takes a heartfelt, if predictable, path to the showdown. You beat Mordegon, and the people you helped put on the road to recovery are free to truly rebuild. Hooray! The day is saved!
Then the credits finish rolling, and Dragon Quest XI's protagonists ask each other, "Okay—but what if we travelled back in time and prevented Mordegon from corrupting Yggdrasil in the first place? We could save a lot of lives, including Veronica's."
Thus, the Luminary decides to bid farewell to his friends in Mordegon's timeline and travel backwards in time to head the evil-doer off at the pass. It works: Mordegon is defeated before he can corrupt Yggdrasil, Veronica survives, and the world remains unsullied.
For a bit.
As per JRPG tradition, you learn Mordegon isn't the only evil being threatening the land of Erdrea. In fact, Mordegon's presence sealed away a bigger, badder foe who descends to say "Howdy" shortly after Mordegon bites it. While Erdrea remains intact in the shadow of this vile newcomer, the land is still in big, big trouble if you don't do something.
The ascent of Dragon Quest XI's true boss—Calasmos—brings a new heap of troubles and trials you can sort out to earn top-notch weaponry, as well as important story interludes. But the best part of Dragon Quest XI's post-game is receiving the opportunity to solve people's problems before they become tragedies in the timeline you left behind. You can save the lovesick mermaid from heartbreak. You can keep the dragon-boy from eating his own mother (shudder). Most importantly, you can keep Veronica in your party, and Serena is left mercifully unaware her sister faded away in another timeline.
Dragon Quest XI uses pain to contrast its moments of healing. The hero's attempt to save the world through time travel and the subsequent unbinding of Calasmos also teaches you there's no single "right" way to recover from tragedy. You can rebuild your life before you fight your demons, or you can fortify yourself and confront them head-on. Both methods are valid.
When you meet the young couple and their newly-baptized baby in the version of Arboria that's untouched by Mordegon's wrath, the mother tells you she feels a distant, strange sorrow whenever she looks at her son's face, and she doesn't understand why. That's Dragon Quest in a nutshell: It hurts you, you forget the agony by the time the next game comes around, and the cycle starts anew. See you next time!