Disclaimer - I do not own Undertale or The Legend of Zelda franchise.
Chapter 1 - The Human Souls
Undyne walks nervously through the Judgement Hall on her way to Asgore, to deliver the final human soul needed for the monsters of the underground to be free. She thought defeating that child would redeem herself, but instead all she felt was guilt. Watching that bag of flesh collapse on the ground after her spear pierced their heart, and exit out the side of their body, she immediately felt regret. "Maybe there was another way," she thought to herself, "What will Papyrus say..." As she stands in the patch of buttercup flowers in the throne room, she feels her body trembling before the king. He looked, sad, and disappointed. She remembered what it was like before, when the queen was still around. Some have speculated she was murdered, others thought she simply went into hiding.
Asgore realizes Undyne standing in front of him. "Oh, my apologies Undyne, I hadn't realized you were standing there. I see you have brought the final soul. Come, we'll open the portal together. Finally, we'll get revenge on those pitiful humans." A sadistic grin appeared on his face.
Flashback
Chara, no please don't go. Alphys please, help her, I don't want to lose her." Toriel was in tears. Her child was deathly ill. All attempts to heal her had failed.
"I'm sorry, my queen, but there's nothing else that I can do. I've tried injecting her With DETERMINATION, I've tried using healing magic, but nothing will work. I'm sorry"
"N-no please please don't take her away." Toriel collapses on the floor, crying. All Asgore can do is put on a blank expression, one of despair, one of the disbelief. Asriel, the prince of the Underground, and Chara's brother, stands by her hospital bread, clenching on to her hand. "Chara, you have to get better. You can't go now, we still have so much to do. You have to get better, so we can play eith Papyrus and Sans, a-and eat butterscotch pie, and watch anime with Alphys." Tears roll down Asriel's cheeks. Chara slowly opens her eyes. "Azzy, is that you? Everything looks so fuzzy." Everyone is in shock, and immediately goes to Chara's side. "Listen, everyone, I'm sorry but it's time for me to go. But before I go, Azzy, I want you to take my necklace, so we'll always be together. Bury me in the fiels of flowers by my village, so I can at least rest peacefully. Goodbye." She closes her eyes, and her pulse slows down until it stops. All that remains is her soul. Asriel, wanting to make things right, takes her soul, and brings her body to the overworld, where her final wishes can be fulfilled. However, the humans did not take kindly to seeing a human child's corpse in the hands of a monster. They slayed Asriel with their determination, and both Chara and Asriel were left to rot in the field of buttercup flowers.
That was the day the King and Queen lost two of their children in a single day
End Flashback
They near the chamber of souls, Undyne was having second thoughts about this. What would happen if they did cross through? There'd be war, and there's no telling if they would win anyway.
"Hey, uh, Asgore. Maybe we shouldn't attack the humans? We already killed 7 of their species, what if we lost?
"That doesn't matter. We'll take down as many of them as possible. It doesn't matter what weapons they have or how much determination they have, as long they suffer for what they've done to us."
As they approach the portal with the 7 souls, Undyne feels something come over her. As the portal begins to open she throws a spear at Asgore knocking the final soul out of place. Something strange happens to the portal. It begins to flicker and swirl, as if it was malfunctioning. Asgore attacks Undyne knocking her back, close to the portal. It begins to suck her in, along with the soul of child she brutally murdered. She disapeears inside the portal along with the red soul, and she falls unconscious.
What do you think she is? A Zora?
Never seen a Zora like her before.
What kind of Zora has hair?
Look at her armor, it looks like it's glowing, in the rhythm of a beating heart.
That'd probably explain the red heart in the middle.
Everyone step aside!
Undyne slowly opens her eyes, and begins ti see strange humanoid fish people? One of them, what appeared to be a young female with red fins, stood by her with her hands on Undyne's armor.
"Who are you," Undyne asked wearily, "Where am I?"
"My name is Mipha, princess of the Zoras and one of the Champions destined to defeat Ganon. You're currently in Hyrule, in the Zora domain. It looks like you've taken quite a beating so I'll heal you."