Why does Robin keep carrying the silver metal box?
Clearly, there are very precious things in that metal box, and that precious thing is actually a Devil Fruit.
This Devil Fruit is the loot that Kahn obtained a few years ago. It is the Paramecia-type Castle-Castle Fruit (Shiro Shiro no Mi).
As the name suggests, the person who eats this Devil Fruit can turn their body into a castle. The user can also shrink any objects, including themselves, and hide them inside their body. If they enter their own body, their outer body becomes a mobile fortress.
In the original story, this fruit was the ability of Capone Bege. If Kahn's parents hadn't been killed, he might have given this Devil Fruit to Capone Bege. But after losing his parents, Kahn saw Capone Bege as a mere tool. So, after obtaining the Castle-Castle Fruit, he decided not to give it to Bege. Instead, he planned to recruit new maids and develop them into his own mobile warehouse.
Now is the time for the mobile warehouse to be born.
Kahn took the Devil Fruit from Robin and looked at Sonia and Mary. "This fruit is a Devil Fruit, known as a secret treasure of the sea. If you eat it, you will gain special abilities."
"The ability of this Devil Fruit is to turn you into a castle. Not only will you have the same defensive power as a castle, but your body will also contain a space as large as a castle."
"If you eat this Devil Fruit, you can easily carry away all the gold here."
"But only one person can eat this Devil Fruit. Sonia, Mary, which of you would like to eat it?"
Hearing this, Sonia and Mary, along with their older sister Hancock, surrounded Kahn.
Looking at the Devil Fruit in Kahn's hand, Mary asked in surprise, "Is this the Devil Fruit that Sister Robin mentioned?"
Sonia was also curious, "Is this the same type of fruit that gives Sister Robin her special ability?"
"If I eat this Devil Fruit, will I have the defence of a castle?"
Hancock pondered Kahn's words for a moment and then said to Mary, "Mary, aren't you focusing on mastering Armament Haki? Then you should eat this Devil Fruit."
"Me? You want me to eat it?"
Mary pointed to herself, then glanced at her sister next to her.
Sonia nodded, "Yes, Mary. If you combine this Devil Fruit's power with your Armament Haki, you'll become incredibly strong and be able to carry all this gold."
Mary looked at the Devil Fruit, then at her sisters and Kahn. Finally, she nodded. "Alright, I'll eat it."
Kahn handed the Devil Fruit to Mary. "Good choice. With this power, you'll be able to help us a lot."
Mary took the fruit, bit into it, and grimaced at the horrible taste. But soon after, she felt a surge of power within her.
"How do you feel?" Kahn asked.
"I feel... different. Stronger," Mary replied, looking at her hands as if expecting them to change.
Kahn smiled. "Good. Now, let's see what you can do. Try storing some of the gold inside you."
Mary concentrated, and soon, the gold pieces around her began to shrink and disappear into her body. The others watched in amazement as Mary effortlessly stored large amounts of gold.
"It's working!" Sonia exclaimed.
Hancock smiled proudly. "Now we really are rich."
Robin observed quietly, pleased to see Kahn's plan coming together. With Mary's new abilities, their group was stronger and more resourceful than ever.
"I also believe so," Sonia nodded in agreement.
For their nine-year-old sister Mary, both Hancock and Sonia were particularly worried. Hancock, in particular, felt an immense guilt for involving her younger sisters in her own curiosity. As a result, she wanted to give the best opportunities to her sisters, especially the youngest, Mary.
Understanding their thoughts, Kahn handed the Paramecia Castle-Castle Fruit to Mary with a smile, "In that case, Mary will be our mobile warehouse from now on."
"I won't let you down, Master."
Mary glanced at the smiling Kahn and Robin, as well as her two older sisters, feeling a surge of warmth in her heart. As a warrior of the Kuja Tribe, she had shed her psychological shadows. With determination, she put down the gold brick she was holding, took the Devil Fruit from Kahn, and resolutely bit into it.
Immediately, Mary's face turned purple from the taste. She made a gagging motion, wanting to spit out the pulp, but Kahn quickly reminded her, "Don't spit it out. Just take a bite; Devil Fruits taste like this."
"...Gulp!"
Hearing Kahn's words, Mary swallowed the fruit with difficulty. She then looked at the remaining pulp in her hand, gasping, "Ha...ha...what kind of fruit is this? It tastes awful!"
"Is it sour?" Hancock and Sonia asked curiously.
"It's not sour. It's a mix of many indescribable flavours."
Remembering the taste, Mary's face turned purple again. She felt unwell just thinking about it. Kahn and Robin, who had experienced this before, didn't laugh at her.
Kahn changed the subject, "Mary, do you feel any changes in your body?"
Hearing this, the three Boa sisters' attention shifted. Mary's face first showed doubt, then joy. "I can feel it. My body has changed a lot...Master, sisters, look at this!"
Due to her limited vocabulary, Mary couldn't fully describe her changes. Instead, she picked up a piece of gold from the ground. Under the watchful eyes of Kahn and the others, she turned the gold into the size of a grain of rice and then placed it into her body.
Instead of merely taking it in, a thumb-sized door opened on Mary's body. Behind that door wasn't a typical body structure but a brightly lit castle. Mary's body had transformed into a castle, complete with its own lights—a miraculous ability granted by the Devil Fruit.
"Very well, Mary. You will be our financial director from now on," Kahn said, smiling with satisfaction as he watched Mary put the tiny gold piece into her body through the small door.
"The inside of her body turned into a building! So amazing!" Sonia exclaimed, then asked expectantly, "Mary, can you put us in too?"
"Hmm...yes."
Mary nodded vigorously and placed her hand on Sonia. In the next second, a transparent white mask appeared out of thin air, and Sonia, wrapped in the mask, shrank at a visible speed and flew into Mary's body through the open door.
"Master, sister, do you want to go in and have a look?" Mary asked Kahn and the others.
"Let's go in and have a look," Kahn nodded, and Robin and Hancock agreed.
So, the three of them became smaller and entered Mary's castle. Inside, they marveled at the incredible transformation, the spacious interior lit up like a grand castle, a perfect mobile warehouse for their adventures.
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