Answer

Don Chinjao considered the words of the young woman in front of him.

She claimed she could do something that so many who were older and more experienced than her failed to do. Something he would have dismissed immediately under normal circumstances.

Mentioning a devil fruit had added some merit to the claim. He himself had long searched for a devil fruit with bone related abilities.

Most of all, this concerned his once proud and pointed skull. And by extension, the treasure his family had accumulated for generations, sitting under the Jewel Ice Sheet, unreachable.

Could he afford to pass up the possibility? He had some hope of Sai one day surpassing him and being able to open the Jewel Ice Sheet instead, but there were no guarantees that day will come.

Could he take the risk? She wasn't strong by any means, but he would have to give her unrestricted access to his head. If she's being honest that she can damage his skull, that also means she could get lucky and kill him too if she's quick enough.

What price would she ask for this service? Would he still be able to refuse after seeing good results?

He discarded the many questions floating around his brain. First he needed to know if it was even feasible.

"Show me your devil fruit ability, little girl. I will see if it is possible to do what you say." He commanded.

Cherry smirked. 'I've got you!'

"My devil fruit is the Fuse Fuse Fruit, I am a Fusion Woman. I can 'un-fuse' the bone, manipulate it into a new position with my special technique, then fuse it back together. I will demonstrate." Cherry said.

She rolled up the sleeve of her left arm and grasped her forearm in the middle with her right hand. Slowly but surely, her left arm seemed to bend in the middle to a roughly 45 degree angle.

"My arm is easy, because my bones are basically just normal bones." She elaborated, as she returned her arm to the original shape. "Your skull is different, I suspect. I'll need to see for myself to be sure. At the very least it's hardness is legendary and I would bet that isn't the only thing special about it."

Sai posed a question. "You said it would be painful, but you didn't seem to be in much pain?"

"That's because I have a near perfect understanding of my own body, Vice-Leader Sai. Your grandfather is another story. Trust me when I say you don't want me to understand his body more than absolutely necessary, either. There are many secrets to be learned by understanding the body. Secrets that can be exploited, if one has bad intentions." Cherry lectured.

Sai and Chinjao were shocked at this revelation and more shocked that Cherry so casually revealed such a thing.

A moment passed in utter silence.

"Hiyahohohoho! This little girl has guts! Alright then, let's go ahead with it." Chinjao made up his mind.

"Old man..." Sai was conflicted. He didn't want to risk any harm coming to his grandfather, a risk that seemed to grow the more he learned about Cherry.

At the same time, something in his gut told him he could trust Cherry and he also didn't want to subvert his grandfather's will.

"Fantastic! We can start tomorrow if you'd like? Tonight's a bit too soon, since somebody left me starving alone in a room all day." Cherry smiled, inwardly celebrating.

Sai flinched a bit at her words.

"I also need to center myself before we begin. Sai, take Miss Harpin to get some food and rest." Chinjao ordered.

...

Cherry fortunately didn't have to sleep on a pirate ship filled with drunkards, but rather had a nice hotel room prepared for her.

Sai came to retrieve her at dawn, much to Cherry's exasperation.

"Why are you waking me so early, Vice-Captain Sai? This is the first time in months I've slept in such a nice bed." Cherry said, rubbing her eyes.

"Oh, my apologies Miss Harpin." Sai said, somewhat confused. He had thought getting up early was only natural as Cherry seemed like a disciplined martial artist.

"Nevermind, let's go. I'm sure Don Chinjao is eager to get started." Cherry once again couldn't stay mad at such a straight forward and honest man.

They walked back to the Happo Navy dock yard after cherry scarfed down a breakfast in the hotel.

They once more entered the captain's quarters of the Happosai to find Chinjao waiting for them.

"There you are Miss Harpin. Let's get started quickly, what do I need to do?" Chinjao greeted.

"Sit however you are most comfortable. I will place my hands on your head from behind you." Cherry replied.

Sai helped Cherry to stack some things forming a place to stand high enough to reach Chinjao's head.

Cherry placed her hands on Chinjao's crumpled skull and sent thin threads of vital energy to examine the skull in detail.

'Remarkable, just remarkable. To think the bones of a human could have such properties. It's similar to the bones of a lesser dragon.' Cherry admired.

Chinjao and Sai didn't say anything or interrupt her. After half an hour, Cherry broke her silence. "I have an idea of what we're dealing with and how to go about remaking your skull. I will begin now, brace yourself."

Chinjao did as she said, but he didn't think it would be necessary. 'It can't hurt as much as when Garp did this to me.' He thought.

He was wrong. Not a sound escaped his mouth, but this was by far the most excruciating pain he had ever suffered.

"Sorry about this, your bones bear a great resemblance to metal. This is good news, as it means the process with go much faster due to their inherent malleability. The bad news is the pain will be orders of magnitude greater than I previously estimated." Cherry spoke nonchalantly.

Chinjao cursed her in his mind while Sai worriedly watched for any signal to stop her from his grandfather.

The session lasted only 10 minutes, but it felt much longer to the two men.

"I think you'll be able to see results in about half the time I mentioned before. I'll see you tomorrow at the same time, Don Chinjao." Cherry said as she clambered down her makeshift tower.

Chinjao let out a long sigh of relief. He was surprised that there was not even the slight ache, or some other indicator of that pain he felt only moments before. The stark comparison to then and now made him feel almost blissful.

"Alright, I will see you tomorrow, Miss Harpin. I hope all is as you say it is." Chinjao stated, feeling his head. He wasn't sure if it was any different.

...

Two weeks later, after the session for the day Chinjao studied himself in the mirror in his room.

He had refused to look at himself or feel his head since the first day. He wanted to see and feel the changes with the greatest impact.

He almost started to cry gazing at his reflection. It was not the caved-in, misshapen skull he was used to seeing, but a rounder more ordinary shape. Sai and his other grandson, Boo, were also nearly in tears seeing their grandfather's former glory returning to him.

"What do you want, Miss Harpin. Just name it, if it's something of mine you will have it." Chinjao stated resolutely. He didn't promise he'd give her anything, he couldn't give her his family's treasure after all. Retrieving that treasure was the primary purpose for restoring his skull to begin with.

"I want to learn your family's martial art." Cherry stated honestly. She had learned these people didn't like dancing around with words.

"Hmmm..." Chinjao pondered seriously. "That's a difficult request. This is my family's secret art."

To be honest, he wanted to just say yes. He was very grateful to Cherry, but his responsibility to his family was of the utmost importance.

"Perhaps..." Chinjao looked at Cherry, then to his grandsons. "Perhaps there is a way to teach you, but there is a condition."

"What would that be?" Cherry asked, with a bad feeling in her gut.