Disclaimer: I do not own Fairy Tail or any of its characters, Hiro Mashima does.
Lucy and Gray were on an S-mission. It was originally Erza's mission but she was in charge of disciplining Natsu and Wendy for destroying Quarto Puppy's headquarters while on a job. So she specially requested Lucy and Gray to go in her place. Lucy was scared of failing the mission. She had heard that one mistake in an S-class mission would most likely cause death. But having Gray by her side calmed her down. They were unaware of the dangers they would face, and the terror of the golden eyed serpent.
Gray and lucy had set off two days ago. Making use of the time to create a possibly effective strategy. Their time limit was one week. The objective was known to be next to impossible, obtaining the golden eye.
They dove underwater on the third day after pinpointing the serpent's location. It was a very heated battle. Most attacks deflected, constant need for air, and their disadvantage of battling in the water caused great trouble to the two. Having being underwater, Gray had to avoid using Extreme Freeze type ice make to avoid turning them both into ice sculptures. Fleuve d'étoiles was rendered useless and Lucy's spirits also found it hard to attack. The serpent's rock hard scales made physical attacks useless. "Lucy! Use Urano Meteoria!" Gray shouted to Lucy. "But I haven't perfected it yet. I could end up destroying everything!" "Just do it! Otherwise we're dead! Gah!" Gray had been slashed by the serpent's razor sharp tail. A deep gash was left and he was bleeding profusely. "Gate of the twins! I open thee!" Lucy screamed,"Gemini! Urano... Meteoria!" That blow was powerful enough that the serpent turned to dust, and only the eye remained.
"Gray!" Lucy swam towards Gray and pulled him out of the water with Capricorn's help. "Capricorn, retrieve the eye and head back to the guild 'kay?" "Yes. For now, get Gray back to the guild. He may not pull through without any treatment." Lucy nodded,"Gate of the Lion, I open thee! Leo!" "How may I be of your service Lu- Woah! W-what happened?!" Lucy opened her mouth to answer, only to be interrupted again."No, save the explanation for later. For now, getting Gray back to the guild is our first priority." Lucy nodded in agreement.
"Oh my god! What happened?" Lucy and Leo came running into the guild, and Mira came running towards them. "Save the explanation for later, we need to do something about him!" "Get Wendy here already!" Gray was at death's doors and was getting paler by the second. Wendy came rushing, gasping at the sight of the wound. "Oh no... I was too late." "What do you mean?" Lucy choked back tears. "The wound is fatal. He also lost an enormous amount of blood. The only way to save him is to do a body condition switch. And that means..." "Killing another in the guild." "No... way..."
Bang! The door was slammed open. Natsu came walking in like an idiot who could not read the situation. "That was harsh... Ouch, my shoulders hurt..." "NATSU!" The whole guild shouted at him angrily. "Nani? Something going on?" Let me rephrase the statement from before. He is an idiot who could not read the situation. Wendy quickly filled him in on the situation.
"A life for a life eh?" Natsu looked towards Lucy. "I'll do it." Everyone looked at him in shock. Natsu and Gray were enemies. Why would he help him?! "Wendy, now before it's too late." Wendy hesitated, tears streaming down her face. But Natsu's threatening words forced her to do it. As wounds starts to appear on Natsu's body, Natsu took off his beloved muffler and handed it to Lucy,"All this is for my beloved Lucy Heartfilia." Lucy was frozen stiff. His words echoed through her mind as more and more wounds took form on Natsu. Natsu started coughing up blood and his face paled. "Natsu!" Lucy shouted. Natsu smiled and whispered, " Sayonara, Lucy... minna san."
Lucy watched as Natsu's lifeless body slumped to the ground. White hot tears leaked from her chocolate eyes. Gray's wounds had vanished and color returned to his face. All the guild members were crying. "Why Natsu... Why..." Back at home, Lucy didn't stop crying. Lucy felt that she needed to convey her last words to Natsu,"Natsu, you were my first love. But I ended up loving Gray even more. Your life still remains in Gray's. We will never forget you... Sayonara, Natsu."
That evening, the bright summer sky had faded away in the most beautiful shade of pink, just like the color of Natsu's hair. It was as if the gods welcomed natsu with open arms, like he was a hero. "Thank you for saving Gray, my loved one Natsu."