Luffy, Zoro and Kiku had just arrived at Bakura Town, they were chasing down a man that had kidnapped Tama. Luffy easily defeated the large group of swordsman by using his haki, and as they were traveling through the town suddenly a sumo wrestler came flying at them. There was a sumo wrestling tournament going on and a man named Urashima was winning. Urashima noticed Kiku and became excited.
"Kiku! Is that you?! Men! Bring her to me!" He yelled.
A group of men picked up Kiku and started carrying her to Urashima. Urashima went to embrace Kiku but she instead draws her sword and cuts his top knot off. In a fit of rage he goes to attack Kiku but Luffy intercepts the attack and starts a sumo match between the two. Luffy easily bested the sumo wrestler and sent him flying into a building.
"Bring me the boss!" Luffy yelled as the audience began to attack him, Zoro and Kiku.
The boss appears sometime later holding Tama. The boss goes by Hold'em and is a large man with a lion head coming out of his bellybutton.
"Luffy, be careful! Kuri region is under Jack's control! Attacking this man could have serious repercussions!" Kiku warned.
A group of people suddenly arrived with a large wagon of food, and Luffy and Zoro decided to steal it. Luffy attacked Hold'em and successfully rescued Tama while Zoro secured the wagon, but while Luffy was retreating he heard about how Hold'em hurt Tama and dropped Tama to finish Hold'em off with a powerful Red Hawk Punch. He then went and grabbed Tama again and leapt on a horse to escape with.
"Hey! What're you doing?!" the horse said angrily.
The horse was actually a Smile user named Speed who had been turned into a centaur from eating a Smile fruit. Tama came up with a plan to calm her by using her powers.
"Kibi… Dango!" the child said and suddenly pulled a dango from her cheek. Her Devil Fruit powers allow her to create dangos from her body and feeding them to an animal tames them for her. She was hoping it would work on a human-animal hybrid too. Luffy took the dango and fed it to the centaur woman and she immediately became happy and compliant. It worked! They rode the woman all the way to Okobore Town, where they delivered the food to the citizens and crushed three gifters who were trying to stop them. They spent some time eating and recuperating before Speed confronted Luffy.
"Excuse me, Mr. Strawhat." Speed said. "That dango was the tastiest thing I've ever eaten! I'd like to repay the favor, so can you follow me to my shop real quick?"
"Huh? Sure, I guess." Luffy said, and followed her to her ship, curious about what it could be.
She led them into the Captain's Quarters.
"So what is it you want to repay me with?" Luffy asked.
"This." Speed responded, and suddenly embraced Luffy with a kiss.
She started swirling her tongue around in his mouth, and for a while it was only her doing anything, but finally the boy followed suit and began to wrestle her tongue with his. While they were kissing, Luffy released her large bosoms from her clothing and began to massage them, squeezing and pulling them repeatedly, before moving to her nipples and tweaking and pulling on them. Some milk managed to escape. The kissing and breast massaging continued for a few minutes before Speed pulled away.
"Now, lay down for me." she said and Luffy complied and played down on the ground.
Speed turned around and backed up so she was standing directly above Luffy, and then suddenly sat down, with her pussy directly on his mouth. Luffy had no hesitation in beginning to eat her out, and Speed quivered in delight. She had eaten a Smile so long ago and turning into a centaur meant she had difficulty getting laid, since nobody wanted to fuck a horse, and this was her first sexual experience since eating the Smile, and boy it felt amazing. She looked down and noticed his rock hard cock and decided to lay down and service it while he eats her out. She was very proficient and kissing and blowjobs, as it was the only thing a guy would let her do after eating the Smile. She deftly swirled her tongue around his cock while moving up and down the shaft. While she was doing this, Luffy grabbed her ass cheeks and started to massage them. He massaged them for a while before he began to spank her. Each slap caused a whimper to escape Speed and she could feel an orgasm coming. She switched to a titjob while sucking the tip and expertly playing with it with her tongue. Each slap brought her closer to cumming, until the final one struck her and she let out a loud moan and came all over Luffy's face.
Speed got up off of Luffy's face and started twerking her butt at him.
"Please fuck me already! It's been so long since I've last had sex! Nobody wants to fuck me because of this horse body!" Luffy started to think this was more a reward for her than him.
Luffy got up from the ground and watched her twerk ass up and dowh. He then grabbed her ass cheeks and started spreading them. Just that alone got an "ohhh~" out of Speed. Luffy examined her ass and pussy. They were undeniably that of a horse's. They exuded a lot of heat that there was steam emanating from them, with lots of juices overflowing from Speed's immense horniness. Luffy then inserted an arm all the way up to his elbow into Speed's horse pussy and started to feel around.
"Oh God yes" escaped from Speed's lips.
Luffy noted that it was very warm and slimy, and much looser than expected for someone who's said they haven't had sex in a long time. Luffy started to think to himself.
"Am I really going to do this? I don't know about fucking a horse pussy, but the poor girl clearly wants it, since it's been so long since she's had sex. Ah what the heck, I've already eaten her out, plus it'll be a unique experience." He then removed his arm and quickly jammed his thick cock into her horse pussy.
"Oh God finally!" Speed yelled in excitement and started neighing.
Luffy activated Gear 2 so he can go as fast and rough as he can. This went on for few minutes before Luffy decided that he needed to be bigger to fill Speed's large horse pussy so he activated Gear 3. His cock grew immensely along with the rest of him and suddenly Speed's horse pussy was filled to the max. Luffy continued the thrusting with his humongous cock while wrapping his legs around Speed's back legs. Speed was going wild, moaning and neighing constantly, she was so happy to finally release all these years of pent up sexual frustration. Luffy decided to increase the stimulation by inserting his tree trunk right arm into her horse all the way up to his elbow. With his other hand he began to spank her again.
The stimulation was too much for Speed. "Oh my God! I'm so full I can't take it!" Speed yelled.
Luffy had the stamina to continue this for half an hour, with Speed cumming every few minutes. When Luffy finally finished she collapsed to the floor. Her ass a bright red from all the spanking.
"Thanks for the repayment, Speed! How about helping us fight back against Kaido? We can do this way more often if you do!" Luffy said.
That was an offer she could never reject.