From the outside, Kingdom Hearts looks like a lighthearted anime romp with Disney characters. Pullling back the curtain, however, reveals a story filled with loss, sacrifice, love, and friendship. At its core, the Kingdom Hearts series is about the connections people make and the influences that one can have on another. The concept of a heart in this universe is like a combination of a soul and consciousness, freely interacting with others without necessarily being attached to a physical body. It might sound wild and weird, but maybe it'll help you understand the darkest moments in the Kingdom Hearts series.
Sora is a kid who just wants to do the right thing, make friends, and protect those he loves.When the first Kingdom Hearts game begins, he is excitedly building a raft with his best friend Riku and his crush, Kairi. Together the trio plans to sail off their island to new adventures. Everything seems to be going well, until Kairi disappears in front of him, Riku is swallowed by darkness, and Sora is attacked by a giant shadow monster.
After that, Sora wakes up in a strange world, holding a strange weapon, learning that his Keyblade means he's destined to save many worlds. While grappling with that knowledge, Sora embarks on a personal mission to find his missing friends. After completing his task, Sora learns that he was never the one that was destined, and then everything immediately falls apart. Sora has his power stripped away, loses his new companions, fights his best friend who has been possessed, sacrifices himself for Kairi, loses his body, and becomes a monster like the ones he's been fighting the whole time.
Sora does overcome this absurdity, is reunited with Kairi, and is now tasked with defeating the man behind all of this: Ansem. After a few grueling fights (for both Sora and the player), Ansem is defeated and the worlds are saved. Unfortunately, there are a few side effects. Having completed his duty and reunited with his friends, Sora loses them once again. Riku is sealed in the Realm of Darkness, and Sora fades is transported to unknown lands. Sora soon finds himself in the mysterious Castle Oblivion, where most of his memories have been stripped away and he must battle against Organization XIII to find out why he's here and what happened to his memories. After awakening a year later and recovering parts of his past, Sora remains hounded by the Organization.
Eventually, by the latter half of Kingdom Hearts II, Sora reunites with Kairi and Riku to face off against the boss of the Organization, Xehanort. Able to finally defeat him, all three friends finally make it back to Destiny Islands with little time to relax. It's not long before Sora and Riku are summoned by Master Yen Sid to take the Mark of Mastery exam. Unfortunately, the exam is sidetracked by the presumed-dead Organization XIII who are using Sora once again for their own nefarious ends. As shown in the Kingdom Hearts III trailer, Sora seems destined to be pursued by these jerks forever.
A Keyblade Master is entrusted with protecting those in needs and keeping the darkness at bay from taking over any world. Under the tutelage of Master Eraqus and Master Xehanort, Aqua finishes her Mark of Mastery exam and gains the title of Keyblade Master, giving her a new suite of powers and knowledge and allows her to teach others the ways of the Keyblade. And then the story immediately dismantles any amount of joy she could have. She is told to track the whereabouts and actions of a good friend resulting in feelings of betrayal and lack of trust.
She also learns that Master Xehanort is behind all the darkness and monsters appearing across the worlds and must now face off against him, standing side by side with her friends Ventus and Terra, on the ancient grounds of the Keyblade War. They fail and fail hard. She loses Terra to Master Xehanort, Ventus falls into what's basically a coma, and she gets lost in the Realm of Darkness. Time moves differently there and she spends nearly a decade wandering before coming in contact with anyone else and her only chance to escape is thwarted by her sense of duty to protect others.
Imagine you're living your life, doing your job, hanging out with your friends everyday, and then all of a sudden the bottom falls out and you find out you're not actually a person and you should never existed in the first place. This is Xion's story. She was the 14th member of Organization XIII, created to house Sora's memories and act as a keyblade wielder. Then she started developing her own memories and feelings.
Once the truth comes out that Xion has become a person, she is constantly referred to as a puppet, told that her memories are false (or outright don't belong to her). Xion eventually learns she must give up her entire existence in order to restore Sora. At first she doesn't want to go, but reluctantly acquiesces because she knows it's the right thing to do. Xion's body disappears and so do all memories of her leaving behind a sense of longing and vague sense of missing to her friends.
In Birth By Sleep, Riku interacts with Terra who entrusts him with the power of a keyblade wielder that will manifest later in his life. Once Riku is older and his powers finally start showing up, he is tempted by darkness that tells him it will make him more powerful. Riku follows this path of darkness thinking it will give him the strength to protect his friends. But the darkness leads to being possessed by Ansem, getting trapped in the Realm of Darkness, and takes away his ability to wield a keyblade.
This curse warps Riku's appearance, preventing him from even approaching his friends. When he does finally confront the people he loves, Riku is still afraid to reveal himself, believing he can and should still solve all his problems on his own. Even after he's freed himself from Ansem, Riku is still haunted by his former tormentor (which makes sense, since we find out later that Ansem never died). is still haunted by Ansem, who we later go on to learn never actually died. In Dream Drop Distance, Riku must finds that Sora is trapped in a deep sleep and now he must once again face off against Ansem, the personification of his inner demons.
"Got it memorized?" is a sentence easily recognized by anyone who's played Kingdom Hearts II. It's the catchphrase of Axel, the fire-wielding, chakram throwing member of Organization XIII. When we're first introduced to Axel, he's talking to Roxas like he's known him for years while Roxas stares at him bewildered. We learn that Roxas was actually the 13th member of the Organization and he, Axel, and Xion were best friends who would always hangout after missions.
After losing Xion and then Roxas, Axel was practically alone. In Birth By Sleep, we learn that before the Organization, Axel was named Lea and states "I want everyone I meet to remember me. Inside people's memories, I can live forever." He doesn't want to be alone and forgotten, spends years losing friends, and works for an Organization that doesn't care for him and dies protecting Sora from a horde of Heartless.
In the entirety of the Kingdom Hearts series, Ventus has lived many lives and all of them have been depressing. In Birth By Sleep, it's revealed Ventus was originally the apprentice of Master Xehanort who was just using him to create a special type of world-dominating keyblade. Failing to transform Ventus to his own ends, Xehanort extracts the darkness from his apprentice's heart. This creates a new being called Vanitas. Stick with us, here.
Xehanort then takes his wounded ward to Destiny Islands to die, but Ventus' heart is unexpectedly healed when coming in contact with a young Sora. Well aware of his protoge's recovery, Xehanort takes Ventus off to train with a keyblade master called Eraqus. This is where Ventus meets up with Aqua, a fellow student. At this point, Ventus has no knowledge of his previous life under Xehanort until later in the game, when Eraqus reveals to him his past.
Eraqus attempts to kill his student, and for a minute there Ventus was actually going to let it happen. Terra steps in and beats Eraqus within an inch of his life, only for Xehanort to step in and finish the job. With his master dead, Ventus reunites with Terra and Aqua at the site of the Keyblade War to face off against Xehanort -- as we mentioned earlier, it doesn't go so well.
Ventus loses his heart, which puts his body into a catatonic state, and his soul basically goes to live within young Sora only to be unleashed when Sora becomes a Heartless in the first game. This is where Ventus becomes Roxas (remember the start of Kingdom Hearts II?) and then proceeds to live yet another life where he is used by others and never told of his past. Ventus/Roxas doesn't even get a happy ending, since he's stored back within Sora so the rest of KHII can proceed. Ventus has had what might be the most fruitless, friendless, torturous life in the Kingdom Hearts franchise. And with this series, that's saying something.