It was silent inside the kitchen of Thousand Sunny. Supper was already over for half a hour and only three straw-hats remained in the room.
You could hear the clatter of the dishes, while Sanji was washing them. He wasn't paying much attention to anything beside that.
Robin meanwhile was reading a book and taking a sip of coffee now and then. Franky was spacing out only sometimes focusing at different points in the room or the books cover, looking like in deep thought.

"Nico Robin? ...", the Cyborg seemed to wake up from his trance.
"Hm?", the eyes of the archaeologist stayed on the pages.
Franky stood up and had a stretch before he spoke again.
"... if you want to try something from that book, for research or something, you can always count on me for help."
He gestured to the book in her hand.

She looked up giving him an irritated glance but couldn't help to smirk.
"Really?"
"Sure. This week I try to be super helpful to all my friends."
Robin really tried to see something like humour or irony in the face of the man in front of her but could only discover honest neutrality.
She did her best to refrain from laughing but the amusement could be heard as she answered.
"That's really nice of you."
"I simply do what I can." He knocked three times on the table and walked out.
"I'm off then. You know where you can find me if you want something."

Smirking she looked after him. As soon as the door closed she started to laugh loudly in her book. She had to close and lay it on the table to keep it safe from the upcoming tears of laughter. Finally she collapsed on the table.
What a nonsense! How atypical!

"Everything all right Robin-chwan?", Sanji gave her confused glance.
"Oh!", she tried to calm down and it somehow worked. "Everything is all right."
Her eyes averted to the book and she started to giggle again.

Outside Franky could hear the black haired womans fit of laughter. It was kind of satisfying and a big grin showed on his face, while he slowly walked to his workshop. Good to know, that this woman could laugh about this kind of stuff. She always seemed distant and to has an affinity to morbid things. Now he could only hope that she would not be angry with him.

As Robin finally calmed herself and convinced the cook that she was fine, she went to bring the book to he women cabin. Today she wouldn't be able to read it any more. From time to time she still giggled and shook her head.
'To help a friend. Doing what he can. Yeah sure.'

In the cabin, Nami was sitting at her table and drawing a map. As the older woman entered, Nami looked up and her eyes widened in confusion.
"What had happened to you?"
The woman in front of her still looked flushed and showed a smile.
"I read."
"And what, if I may ask?"
Robin showed the younger girl the books cover.
"'How to use Tantric Sex for enlightenment'?", Nami read disbelieving and showing a light blush. 'What the hell?'

Robin nodded and had to bite her lip to not start to laugh again.
Nami only looked at her with huge, confused and frightened eyes.
Better not ask.

Okay. So let me explain a little bit.
Maybe Robin and Franky seem a little OOC. If you think so: I'm sorry.
But with Franky it was kind of intentional. Taking in consideration that Robin would rarely laugh at something that tries to be funny (Can you imagine Robin laughing about a Clown? See? Me neither). I can't see her that way. She does have a very bizarre kind of humour, and that is why Franky would need to act bizarre (bizarre for his kind). Also... I'm sure Robin does drop her distant way from time to time and is not immune to fits of laughter. Especially since the is on board of Sunny. She got more laid back. So, why not laugh about THIS KIND OF STUFF?
As for the book I can imagine her to read about this topic. Not because of the Sex but the philosophical teaching. Okay, maybe because of the sex too.

At first I wanted to make her read the Kama Sutra but I'm not even sure if there is text in it. And since there is more to Tantric-Sex than different positions, but philosophical stuff and meditation and blah, blah, blah. It's something Robin can actually READ. xD

Enough talking already. I hope you had fun.

PS. English is not my mother tongue so bear with me. Still I'm happy about any correction that slipped my double checks.