Blue Iris; Sanji X! Neko Reader 

Zoro and Sanji looked at each other.
"Hey, would you lend me ya hand for about 10 seconds?" Sanji asked.
"Sure, a fair deal to me," Zoro answered as he jumped off the railing to dive into the water. 

(y/n) just stared at the ladder then looked at Zoro. Zoro grabbed (y/n)'s waist and looked up.
"ERO-COOK!! YA READY!!" Zoro yelled.
"READY!!" Sanji replied from the ship.
"CATCH!! MUTORYU TATSUMAKI!!!" 
With that (y/n) went flying in the air. 

"KYAAA!!" was what she wanted to scream but nothing came out. 
Before she noticed (y/n) was already in the hands of a prince. He then went to the tank room and put her in it. (y/n) happily swam in the water. 
"The tank in the ship isn't that bad. The blue colour of the sea was better though." (y/n) said to her self.
But then she was plucked out by Sanji and was pinned to the deck. 

"(y/n) get a hold of your self. You need to be back to normal!" Sanji shouted. 
"Huh? I am normal." (y/n) questioned.
"Normal? Look at your hands. There is a thin layer of skin connecting each finger. Your (s/c) skin is turning paler and paler. Your (h/c) hair is turning golden and now both of your eyes are blue." 
(y/n) looked at them.
"Isn't that normal? I mean I am a fish after all." (y/n) replied. 

Everyone had their eyes widen. Everyone came into the room. A straw hat that was on Luffy's head covered his eyes. 
"Brook. We are going with your idea. I wish you luck (y/n)" Luffy said. 

His voice was deep. Deep enough it sent shiver down (y/n)'s back. (y/n) was clueless.
"Sanji... Can you put me back in the water. It's getting hard for me to breath." (y/n) asked. 
"No, we aren't going to let you," Luffy said. 

(y/n) now understood. She was panicking now. She started to wiggle out of Sanji's grasp and wiggled the way to the tank. 

She was stopped when a sword got stabbed in front of her face. Nearly cutting a bit off her nose. 

"Even though you might be related captain orders," Zoro grumbled.
(y/n) then forced her self to move away from Zoro and towards the tank lid.

"Campo de Flores; Wall!" Robin yelled. 

A row of arms sprouted blocking (y/n)'s entrance. But (y/n) simply slithered through the gaps. But Franky had just closed the lid. Now (y/n)'s only way was to get out the door. 

(y/n) kicked the wall to use a lot of force to push through everyone. 

"Sumanei! GOMU GOMU NO JET PISTOL!!" Luffy yelled. 
(Sumanei = Sorry in a short form)
"YAHATSUGIRI!" Brook yelled.
"THUNDER TEMPO!" Nami yelled.
"BRAIN POINT!!" Chopper yelled.
"GYORIN! (Fish Scale)" (y/n) yelled.
A golden scale appeared in front of (y/n) blocking the attacks. The attacks were blocked and (y/n) was moving forwards. Her legs were now becoming a tail. A mermaid tail. Sanji had no choice now. 

Sanji kicked the ground making (y/n) fall into it. Sanji jumped in and stopped her from moving.
"Campo de Flores; Wall block," Robin yelled.

There was no escape now. Sanji and (y/n) was in a square. No place to escape. 
"HIRE BLADE! (Fin Blade)" (y/n) yelled. 

The fin that now grew on (y/n)'s arms turned to blades to cut open her path. But before the blade could touch the skin Sanji got in the way. The blades turned back to fins before it came to contact. 

"Sanji. Please let me breathe." (y/n) pleaded.
Tears fell down her eyes.
"Does it not hurt you all? The pain I get!" (y/n) yelled.
It hurt for all of them. They could see but their eyes were filled with tears. It hurts to hurt a Nakama.
"It does hurt us. So please trust us!" Sanji yelled. 

(y/n) was taken back. But then accepted.

"I hope your 'plan' works." (y/n) muttered as she leaned against the arms. 
Sanji then grabbed (y/n) by the arm and hugged her. 
"If we do fail at least you'll remember us," Sanji said as he kissed. 
Whole French kiss.

(y/n) eyes widened but then accepted him. Either die without remembering the true hearts of her Nakama or die remembering the pain. Sanji was close to having no air but did his best not to show it. (y/n)'s (s/c) skin was coming back and even also her (h/l) (h/c) hair. (y/n)'s  grip tightened on Sanji's shirt until she lost consciousness. She died. 

(y/n) became limp in Sanji's arm. A smile plastered on her face.
"Where is her soul, Brook?" Luffy asked.

Brook shook his head and then his body became limp. Tears started to flow from everyone.
"I'm sorry we killed you (y/n)!" Luffy cried, "I should of let you live like a mermaid."
Tears flowed even down Zoro's cheek.
"Sis...." he grumbled.
Sanji grabbed and hugged (y/n)'s body. 
"Please come back." Sanji cried. 

*Plink* *plink* *plink*

Went the tears of the Nakama as it fell down their faces. Until Sanji's eyes widened.
"WHO SAID I WAS DEAD!!" (y/n) yelled as she jumped to the deck and punched Luffy so his face slams into the ground.
"(y/n)!!" Luffy yelled after he pulled his head out of the hole.
(y/n) stood with a big cat smile with her (f/c) tail and (f/c) ears twitching. (h/l)(h/c) hair and (e/c) iris. 

"Good morning." (y/n) smiled. 

Luffy jumped onto (y/n) causing her to fall into the hole again but this time with a lot of weight.
"Doggy PILE!!" Luffy yelled.
"Welcome back (y/n)!" everyone else cheered as tears fell down their faces.
Sanji was the only one that wasn't in the group. 

"Hey, Brook why were you shaking your head then?" Sanji asked. 
"I was just looking for (y/n)-san's soul. I didn't shake my head," Brook replies. 
"HOW WERE WE SUPPOSE TO KNOW!! IT'S CONFUSING!!" Everyone else commented except for Luffy.
"Shishishishishi!" Luffy laughed. 

When (y/n) was able to go out of the doggy pile she finally spoke. She stood in front of him. 
"That answer, by the way, is yes, I would love to!" (y/n) replied with a smile.
Sanji instantly jumped higher than the sky. 

"Yeahs!!!!!" he shouted.

#FLASHBACK#
(y/n) was already out of air. She was going to die any second. When Sanji pulled away.
"If you could live another life would you be my wife?" Sanji whispered.
(y/n)'s eyes widened more than a fish eyes could.
"It might be a bit early but-" with that, she fell limp.
#END#

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Just to clarify, (y/n) was Zoro's sis so he accepted to help Sanji. Want a part 3?