Kingdom Hearts, a summary: Intended for those not familiar with the series.
There was a war because of selfish people wanting to have more light than others. A ton of people died trying to become the controller of the source of light, called Kingdom Hearts.
Hella years later the war is forgotten by most but this guy, Master Xehanort, does some research and thinks he’s found a way to gain control of Kingdom Hearts so he separates his apprentice into two parts and has them fight each other to create the key to the light.
But since he’s old and wants to be young again, he also decides that he’s gonna put his heart(soul) inside his apprentice’s best friend since that friend has a knack for Darkness powers like he does.
His plans fail and he ends up with amnesia. While amnesiac he becomes an apprentice to Ansem the Wise who wants to help cure his amnesia so Ansem decides to start experimenting with hearts(souls) and Darkness. This ultimately causes Xehanort(the old asshole) to be split into two parts. One of them calls himself Ansem, the other calls himself Xemnas.
Both of them still want to gain control of Kingdom Hearts so they both make fabricated doors to Kingdom Hearts. Ansem makes his from the Hearts of a bunch of worlds, and Xemnas makes his from the hearts of hundreds of thousands of living beings who became Heartless.
Sora(the hero) stops them both, and even kills them, causing them to recombine into Master Xehanort. He’s now been stopped three times but since he has back up plans on top of back up plans on top of black up plans he also had Ansem contact his younger self in the past and give him special powers in case all his plans failed.
His younger self then travels throughout time gathering thirteen vessels to all be part Xehanort. The true doorway to Kingdom Hearts requires a key made from thirteen pieces of Darkness and seven pieces of light. So he’s decided to be more patient and less hasty, he’s going to make a team of Xehanorts and they’re gonna fight against a team of seven good guys to create the key he wants. So far we know the identities of six of the Darknesses(Master Xehanort, Young Xehanort, Xigbar, Saix, Ansem, and Xemnas) and all seven Lights(Sora, Riku, Aqua, Kairi, Lea(who everyone calls Axel), Ventus, and King Mickey).