A/N: this happens before the main story "True Friendship Never Dies" even begins. and end at the beginning of the chapter: Dancing Waters Forming Bond.
hope it help :)

_

"the Real of Darkness is a dangerous place, especially for those who doesn't have a resistance." My voice echoed in the room there has been my home ever since my escape from Castle Oblivion, it looked very alike the room I was trapped in, still this place gave me a form of safety. The drawing before me is just finish and thus the memory inside of it. I´ve almost used all my black colors to this one. The memory of the Dark Realm, but not only the journey inside of it. In the drawing is a boy in a black and red bodysuit. Very alike to the one Riku used when he was controlled by the darkness. Except…
"this boy… he looks like Sora" but why? I couldn´t help but look out at my window, for this could very well still happen inside the Realm of Darkness. A small sight escaped my lips "In search for one of the missing Keyblade Wielders who secretly started out your own way to her isn´t easy…" I eyed the drawing again, that boy… and that hooded man hidden in the darkness.
"he used Sora´s weakness against the darkness to awaken a dark being, somehow been trapped inside of him, but…" where did this dark being come from?

_

Mickey stopped on the road inside the Realm of Darkness, staring with narrowed eyes down at the dark path, already holding his keyblade in hand, the same keyblade he gained inside this realm. Riku and Sora quickly joined him after have stepped out from the portal there lead them to this world, the newly named keyblade master; Riku turned around and closed the portal. He wasn´t much for it, but he has been forced dwell into the dark powers again in order for him and his friends getting to this place. With the portal closed, he turned back to Sora who looked around with a mix of dread and awe. Riku took a look around himself; this valley was as dark as the names itself, the only changes of the dark colors were the many cracks in the cliffs where some strange blue light resided. He turned away from the scenery and took the lead "let´s go"

"right" Sora nodded and without hesitating followed. Mickey did as well, although, like Riku was quite wary. Him and Riku has seen what danger lurks in this place and the keyblades was a huge magnet to the residents to the Realm of Darkness.
it did not take long before they encountered a known enemy: the Heartless and all of them were strong, this was their realm after all. And no matter how many they struck down, more came to take their place.
Mickey struck several Nova Shadows down with his acrobatic jumping and landed not far from a strange orb of darkness, he eyed it for a second, before using the orbs pushing powers to his advance and took down a small horde.
"this way!" he called for Sora and Riku and used the orb to get to higher levels and thus closer to their goal. The two boys followed him and although they had Heartless around them, they did barely stop to fight them. The determent trio only did stop if they got surrounded. The further they got inside the realm the more Riku felt they got watched; still he knew that if he stopped, they could get in more danger than they already were in.
they only stopped at a road with waterfalls of darkness around them, here it seems that there wasn´t as many Heartless around and allowed them getting a breather.
Riku eyed Sora once, asking "you doing alright?"
Sora nodded, although he did look a little strained from the pressure the darkness put on him "don´t worry about me"
Riku simple nodded, still he couldn´t help but worry; Sora might not tell it, but this realm takes a lot of strength. He did not have Riku´s resistance to the darkness. it made the young master wonder.. he turned his eyes to Mickey and the small king smiled weakly back, although it was more in worry for their safety. The king did not look the slightest strained being here, proving his strength just by that, Riku was happy they had Mickey here.
Riku turned back to the path, well knowing there was only one way to their main goal, someone was waiting for them, still the nagging feeling of being watched did not help "we better move" he suggested and they moved on. on this path Riku went up beside Mickey, and Sora "I don´t think we´re alone" he said and Sora gave him a slight surprised look and asked "you mean the Heartless?"

"no, something else"

Mickey nodded slowly, admitting "I feel it too" he looked seriously up to the boys "I fear it´s one of Seekers" he looked over his shoulders, slightly hoping he would catch whoever stalked them in the shadows.
"Xehanort would know we would try and save Aqua"
"but if he knows, then why don´t he try and stop us?" Sora asked, like Mickey, trying to see if someone was around in this one route path. Riku was the only one who didn´t, but his senses were on high alert "because it is not time" he simple said, added "we should get going, stay alert" he told mostly Sora.
the brunette nodded.

they arrived to a huge open space area, covered in a thick dark mist. They walked through the valley, only meeting the usual horde of high level Heartless, but then, Riku stopped to a halt, for right in that second; he sensed a way to familiar scent. He gasped turned around, just as a dark figure appeared and aimed right for Sora.

"Sora, watch out!" Riku called. Sora eyed him with a gasp, turned around and blocked the attacker in the last second. The weapons slashing against each other echoed through the realm and the hooded landed not far from Sora who turned around to him, angry of the sudden attack and ready to fight him if necessarily. Mickey attacked first, but only got a mirage of the person, the hooded appeared again, this time taking the hood down and revealing it was the young vision of Xehanort.

"you sure has quick reflexes" he said with his piecing yellow eyes on Sora who kept on glaring. Young Xehanort turned to Riku "and I see you have once again taken hold on the Darkness, yet, it barely touches your heart"

"Xehanort!" Mickey called angry, pointing his keyblade from this same realm against him "are you here to stop us?"

"far from" Young Xehanort said in a somewhat amused voice "it´s about time she will join this battle, you need another Guardian of Light" his eyes suddenly darkness "just as we need to rejoin our Seekers of Darkness"

"there one here?" Sora asked rather clueless.

Young Xehanort gave him a small smirk "in some way, there is a reason why my future self allowed you go this far, for only in this realm, it would succeed." he pointed at Sora "of releasing one of the prisoners inside your Heart!" he called his keyblade and faster than the eye could see, he struck Sora.

"Sora!" Riku called as his friend fell on the ground, unconscious but seemly alright beside from that. the young keyblade master ran towards his friend, but Young Xehanort stopped him, just like he did in The World That Never Was.
Riku got away in the last second before he got struck by the keyblade of time.

"don´t worry about him, Sora will be fine" Young Xehanort ensured, he turned around as Darkness escaped the boy and formed another body. "I can´t however say the same for you" the darkness faded away and before Sora stood another boy, the face couldn´t be seen because of a mask, but the body suit told more than anything than this stranger was on the side of Darkness.

Riku sneered, feeling nauseous of the pure darkness this boy gave of.
the masked boy eyed Sora, before looking at Mickey, fully knowing who this was.

"you?!" the King asked in disbelief. "didn´t Ventus take care of you?!"

"ahh Ventus" the boy spoke as he went past Sora, completely ignoring him. "that idiot almost destroyed us both with that stunt he pulled off" he turned to Xehanort, but when Xehanort didn´t do anything, the masked turned back to the two wielders "luckily, this kid saved Ventus, and thus: me" a keyblade appeared in his hand, much to Riku´s shock "a keyblade?!" however he quickly got over the shock and went in battle stage, he have to fight this dark being, still... he also needed to help Sora.
"Mickey"
the small king looked up to him and Riku asked, well knowing he wouldn´t be able to fight if he also have to protect Sora "help Sora, I got this one"

Mickey nodded "good luck" and he ran over to the still unconscious Sora.
The strange boy made a small huff "fine, let´s see what you´re made off" and he attacked.

Riku quickly blocked the attack and retaliated with a dark fire ball. It surprised the masked quite the bit, then he chuckled devilish "finally someone with a back bone" and the true battle began, like Riku, this boy could use darkness, but to such an extent than Riku doubted that this boy had any light inside of him. Every element he used was out of darkness and Riku was quite happy that he too controlled that power and had the resistance for it, for if he did not: then he would have been in big trouble. For someone who has just been created, this masked boy sure could pull a punch. It was mere luck that Riku defeated him and tore the mask off him in the progress.
The boy landed hard on the ground, but did however quickly get back up again. Riku gasped of what he saw what has been behind the mask.
the boy smirked to him, almost happy seeing the shock on Riku´s face "do you see what I´m truly is?" he asked.
Riku did not answer; he was still shocked seeing Sora´s face on this pure being of darkness. only difference was the dark hair, slightly lighter skin and those cruel yellow eyes, showing nothing but negativity emotions in them. Was this boy… the darkness of Sora?
in his shocked state, he didn´t see the danger before it was too late. The dark Sora have used his stunned moment to his advance and fired a powerful dark spell at him, it would have killed Riku if not for his dark shield and resistance to the darkness.
Riku fell on his knees, gasping of the power behind this blast. He only stopped when the dark boy stood before him, smirking down to him. Still smirking gleeful; he lifted his keyblade, about to make the final blow, but got stopped.

"Vanitas"

the dark vision of Sora growled turned to Young Xehanort who finally chose to intervene "leave him" he ordered Vanitas, but the dark boy looked like he really wanted to refuse "you´re not the boss of me" Vanitas sneered and turned back to Riku.
the young keyblade master got slowly on his feet, just as Young Xehanort told harshly Vanitas "obey or return back to the void" for the first time since the mask came off, Riku not only saw fear in those yellow eyes, his whole body almost trembled.
Whatever this "void" is, Vanitas feared it more than anything else. Vanitas eyed him, the fear was gone once again, the ignorant attitude returned "consider yourself lucky" he growled, turned on his heels and left with Young Xehanort.
Riku let out a long sight of relief; he had never expected fighting a darker side of Sora.
less in the realm where those of the darkness has the greatest advantage. He turned to Mickey and Sora who has more or less regained conscious, the worst was over, and still this journey was not done.
Sora sat up, having a face of being clueless. Riku wondered if Sora has forgotten what has happen, maybe it was for the best, for he wasn´t sure how he should explain this. Mickey exchanged a few words to Sora, before going over to Riku
"you alright?" the small king asked.

Riku nodded "yeah… your majesty?"

"hm?"

"please don´t tell Sora about this"

Mickey blinked, but did not argue, he knew Riku´s reason "gosh" he crossed his arms with a sad look "I would never have thought that Vanitas resided inside of him, of all people"

"you know him?" Riku asked and the small king nodded although admitted "I´ve fought him a few times with my other friends, but… this is the first time I have seen his face"
Riku nodded, still shocked of what face has been underneath that mask.

Finally arrived to the Dark Margin, finally seeing one of the keyblade masters from the past, one of Mickey´s friends. This woman was quite beautiful. A determent yet kindhearted keyblade master.
but she wasn´t alone. Sitting on a rock, another hooded was. but this wasn´t one of the Seekers. To the trios great surprise. it turned out to be Ansem the Wise. He had survived the blast, but didn´t get away unscathed. His memories has been scrambled and could barely recognized any of them, the only one he seems to recognize was Sora.
Mickey was quite sad at this, although he was also happy that his old friend has survived. Also very happy that even been trapped for so long in the Realm of Darkness, the woman Aqua was safe and sound, determent to help them in any means.

_

I walked over to the window, not holding back the smile of a happy memory to this darker one. even Ansem the wise has not been very kind to me, I still wish I could help him. but sadly… I can´t restore Ansem´s memories. Sora and Riku lead Ansem back home and trusted that Ansem would get a better life, and his once again good hearted apprentices could care for him. I´m sad about his scattered memories, but happy that he at least don´t have to be alone anymore.

I hugged another newly made drawing, showing what happening right in this very moment. It was the kyeblade wielder Aqua talking to Sora, Riku and Kairi in the tower of Yin Sid
"Ventus has been sleeping inside of you. he´s in Castle Oblivion" I smiled, somehow feeling happy that I wasn´t alone back then.
I need to go back to that place, maybe see if I can help them. I went past the drawings, hesitated a little at the memory of the masked boy, Vanitas. Should I tell him?

I smiled weakly left the room "not today"