Along with the written story I’m going to post here, I recorded all the cutscenes of the game from each caracter and put them together in the order I thought fit best according to the timeline. It will obviously be posted in several parts because the all the cutscenes together is like 5-6 hours worth of footage. I’ll post the videos that are relevent with what I write here so you can watch them if you need more details (or if you just want to skip reading what I wrote and just watch it happen haha)
In the Keyblade Graveyard, Terra admits to Aqua that Xehanort used him to strike down Eraqus, all so Terra’s darkness would awaken. When Ven arrives, he explains what the X-blade is and asks them to put an end to him so that it can never be forged. Before Terra and Aqua can do anything, Xehanort and Vanitas make their entrance. Terra jumps to fight Xehanort, but Xehanort lifts the part of the ground he’s standing on. Vanitas then floats on multiple Keyblades that are in the graveyard and starts attacking Aqua while Terra is being circled by Keyblades. Aqua manages to free Terra and he lands in front of Xehanort. Ven tries to attack Xehanort, but Xehanort grabs him by the head, freezes him and drops him off the cliff.
While Terra fights against Xehanort, Vanitas is instructed to go take what Ven owes him and kill Aqua. Enraged by Xehanort’s actions, Terra gives in to the darkness. At the bottom of the cliff, Braig challenges Aqua. Right before Aqua finishes him off, Braig says he must have bough him enough time and runs off. At this moment, Vanitas jumps down the cliff and knocks Aqua down. Angry, Ven manages to unfreeze himself and fights against Vanitas. Once Ven got the upper hand and Vanitas’ body is about to give in, Vanitas starts revealing where the Unversed came from to finally merge his body with Ven’s and forge the X-blade. At the top of the cliff, Terra was about to finish off Xehanort when Xehanort sees the pillar of light revealing the X-blade had been forged. He unlocks his heart and sends it inside Terra before Terra can react. Terra’s armor falls off and we see his body now with white hair making Xehanort’s Keyblade appear in his hand. Before he can walk away, a barrier is made and Terra’s armor stands. Terra’s mind now battles against Terra-Xehanort and knocks him down. Sadly, he doesn’t take control of his body back before being engulfed by a circle of light. Terra’s story ends with him thinking “One day I will set this right”.
Aqua wakes up with Mickey next to her. She quickly remembers Ven was in trouble. Seeing him on top of a platform, she thinks he’s okay, but he doesn’t answer her calls. Mickey immediately recognises the X-blade and is ready to defend Aqua when Ven-Vanitas attacks her. Tired of hearing Ven-Vanitas go on about his plans on starting another Keyblade War, Aqua and Mickey fight against him. After being knocked down, Aqua holds her Wayfinder ans asks Ven and Terra to give her strength. Her Keyblade starts to shine and she is able to defeat Ven-Vanitas, making the X-blade go haywire in the process. Ven returns to his normal appearance and Aqua tries to reach him while shots of light are flying everywhere. She flies after Ven to grab his hand and they sent in the Lanes Between by the flash of light. Inside Ven’s heart, Ven fights against Vanitas some more to destroy him completely, knowing that in the process, he will destroy himself. Ven wins and finds himself inside someone else’s heart. Meanwhile, Mickey grabs on to Aqua and Ven’s bodies in the Lanes Between and brings them to Yen Sid.
Yen Sid informs Aqua that they couldn’t find any signs of Terra. He then tells her Ven’s heart is sleeping and he doesn’t know when or if he’ll ever wake up. He informs her that Ven’s heart sleeps between light and darkness and that what he needs is for his friends to believe in him and love him so that he can find his way back to the light.