"Kuhahaha!"
Loud laughter filled the quiet, sealed cave. "I never thought I'd see something this crazy!" Veldora, the Storm Dragon, the fourth True Dragon, roared with joy. "As far as I know, a True Dragon only appears for the first time in the Palace of the Beginning, where my older brother woke up!"
He looked at the being in front of him with wide, amazed eyes. It was a new True Dragon, glowing azure blue, like a brother to his own stormy self. This "little slime" he'd met, this odd friend he'd named, had now become the Fifth True Dragon. It was impossible, but the huge power Rimuru gave off proved it. Veldora's face, that was dumb founded, now showed a wide, happy grin. Finally! A younger brother! Maybe just maybe now my sisters will stop bothering me and pay attention to him. And a new friend too! kuhahaha My best friend!
As Veldora laughed, the blue dragon began to change. Its giant form shrunk, twisted, and became something new. Where the dragon was, stood a human, beautiful in a way that seemed almost divine. This person had silver-blue hair, bright golden eyes, and was slim but tall.
It seems I've merged with my past self, Rimuru thought to himself. He wasn't from this time. He came from the future. Back then, he was just a slime, but a very strong one, as powerful as a Demon Lord. He was killed by someone from the Eastern Empire during a big war. When he was reborn as the Fifth True Dragon (which he always was, but had been sleeping), he saw a world mostly destroyed. He found his beloved dying, who raging with sadness over losing him. The Lord of Darkness had to stop her to save the world. So, Rimuru sent her mind, and his own, back to the distant past, to the time he first came to this world.
I thought I would only remember the future, Rimuru's golden eyes glinted, but I have my power too. Good. This gives me a better chance to fix everything this time.
Shaking off these deep thoughts, Rimuru looked at the giant Storm Dragon, his first friend in this world.
"Well," Rimuru said, his voice calm but firm, "it was a surprise for me too, Veldora. Becoming human, then a slime, and now... this. Are you ready? I'm going to put you in my stomach ahh well Imaginary space I guess it's called now ."
Veldora gasped. "Hey! Don't be so rude! You should call me 'Big Brother,' you know!"
Rimuru's perfect lips curved into a small, playful smile. "Big Brother my ass."
"Ehhhh?!" Veldora yelled, shocked.
"Don't 'ehhh' me," Rimuru shot back, stepping closer. "Start getting ready in your head. I need to study your magic barrier carefully before I can truly let you out."
"Oh, I'm ready! No problem!" Veldora announced, puffing out his chest. "But Rimuru, you're so strong now, can't you just let me out right away?"
"No, I can't," Rimuru lied smoothly. "The barrier is stronger than I thought, and I can't use my full power yet."
"Oh. Well, that's too bad," Veldora grumbled, but his excitement quickly returned. "No matter! I'm ready! See you after the barrier is broken and I'm free! Kuhahahahaha!"
"Okay, here I go." Rimuru held out his hand. A swirling blue energy opened up, growing fast. It pulled Veldora's huge body inside, sending him easily into Rimuru's Imaginary space.
To be honest, Rimuru thought, as the last of the blue energy disappeared, leaving the cave suddenly silent, I could free him easily right now. But... no. Veldora should stay there for a bit. I don't know what he'd do if I let him out right away. I need to get everything ready first, then I'll release him. His golden eyes, holding the sadness of a broken future and the cleverness of a reborn True Dragon, looked into the empty cave. The real plan had just begun.
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Well It was the first chapter I know it's not well written but I wasn't able to figure it out how should the first conversation should start and also it didn't write the past story as it will be reveled in later chapters