Twilight was deep in her thoughts as she walked through Ponyville. It had now been almost a month since the start of her experiment. She had to admit that things had gone better than she could of ever expected. Rainbow Dash had been gaining steadily. In addition, Twilight's weight gain spells seemed to be getting more effective all the time. The magic expo wasn't for another month and she was already near guaranteed to win.

She had made sure to finish up all her notes early since it was going to be a big day. It was Rainbow Dash's birthday, and as usual Pinkie Pie was throwing a huge party. Like a typical Pinkie Party there was going to be calorie rich sweets everywhere. It was the perfect stage for Twilight to continue accelerating her experiment.

Twilight entered Sugarcube Corner with great excitement. Everypony was there. Including Rainbow Dash's other four best friends,Spike, and some other assorted guests from Ponyville that Pinkie Pie had invited. Now they just had to wait for the guest of honor.

Twilight was approached by Pinkie Pie, who seemed more excited than anypony,"Twilight! You're here! We're almost ready now."

"I've got to say Pinkie, you've done a great job setting this up," Twilight complimented as she took a look around Sugarcube Corner. The entire place had been transformed with vibrant colors and decorations. There were more balloons than ponies. Most importantly, there was an over abundance of party food. Not only was the main counter covered with food, there were several tables full as well! Under normal circumstances a lot of this would end up going to waste. Considering who the party was for though.....

"Thanks Twilight," Pinkie replied,"Feel free to sample some of the food. Just don't eat any of the giant cake I have stashed behind the counter. We need to save it for Dashie."

Twilight nodded as she strolled over to the main counter. Eyeing the assortment of delectable brownies,cupcakes,cookies, and much more. She grabbed one of the cupcakes and took a bite. She was immediately awarded with an intense flavor of chocolate mixed with cherry. A similar taste test of the other categories of treats revealed them all to be equally tasty. Twilight herself could barely resist the food here. There was absolutely no chance of Rainbow Dash having the willpower to resist.

"Dashie's coming everypony, get ready!" Pinkie Pie shouted.

Twilight quickly found herself some cover behind a table as Pinkie Pie shut off the lights. A few moments later the door opened to reveal Rainbow Dash. This led to Pinkie Pie flicking on the lights and everypony leaping out of their hiding spots to yell "Surprise!". Twilight joined the rest of her friends in walking up to Rainbow Dash to congratulate her up close.

"Happy birthday Dashie!"Chimed Pinkie,"This is gonna be the best party ever! We've got a giant cake, and we're gonna have a pinata, and games! Lots and lots of games!"

Rainbow Dash laughed happily, "Thanks Pinkie. This looks really awesome. I'm not even sure where to start."

"Well, ah'll let you have the run of the place first, but sometime ah gotta take ya on for that eating contest rematch. Ah probably lose, but ah gotta try,"challenged Applejack.

Rainbow Dash looked as confident as ever, "You're on."

While the others were busy talking with Rainbow Dash, Twilight took it upon herself to examine Dash's ever expanding form. Her belly hung down just a little past her knees, and wobbled like jello when she moved. Her neck had thickened quite a bit. Leaving her with an undeniable double chin. Her front legs seemed to be following the example of her rear legs and were plumping up as well.

"Well, better not waste any time. I've got a lot to do!" Rainbow Dash stated.

"Right, Dashie,"agree Pinkie before addressing the whole crowd, "Let's get this party started!"

All the energy that had been building up before the party exploded. Soon the room was filled with the loud sounds of ponies partying as all the guests sought out ways to entertain themselves. Meanwhile, Rainbow Dash began waddling towards the counter. This gave Twilight a perfect view from the back. Rainbow's thighs were extremely thick. To the point where they were rubbing together constantly. However, this was nothing compared to the amazing growth of Dash's flank. Two large, round,and soft plot cheeks curved out the rear of her body. Her rump didn't just jiggle, it bounced. Every step caused that rear to shake enticingly. Twilight had to close her jaw and keep herself from drooling as she began to fantasize. How lovely it would be to caress and rub that soft,squishy flesh...

"Twilight!"

Twilight jumped slightly as her day dream was interrupted. She saw Pinkie Pie standing in front of her, looking a little curious. "Huh? What is it, Pinkie?"

"Were you staring at Dashie's flank?"

Twilight could feel her face turn hot as she stammered for words to cover herself,"W-What? No, of course not! I was just..uhh...I..."

"Pffft, you were! Don't worry Twi, I won't tell anypony,"Pinkie assured Twilight with a wink before going over to Rainbow Dash's side to suggest what flavors of sweets to try first.

Twilight let out a sigh of relief."That was a close one". She had to be more careful. If Dash would happen to catch her getting so enthralled she might start to get suspicious.

Meanwhile at the counter Rainbow Dash was getting well acquainted with the assortment of sweets created in her honor. She first confronted a plate of cupcakes. It started with just one bite of a blueberry capcake. Then that bite turned into the entire cupcake being shoved into her maw. Before long she had consumed the entire plate, filling her mouth with several cupcakes and a variety of fruity flavors. She had already consumed more than any other pony at the party and wasn't even close to feeling full. She quickly moved on to a plate full of cookies, shoving down nearly a dozen in just a few minutes. It wasn't until a half plate full of thick,creamy,double fudge brownies later that she started to feel full. She was ready to call it good when just shortly after stopping she felt a sudden emptiness in her stomach. It seems she still had more room left than she thought. Before she had time to question it Pinkie Pie went behind the counter and pulled up what had to be the most delicious looking cake Dash had ever seen.

Hefted on to the counter was a towering,quadruple layered chocolate cake. Just the look off it was irresistible. It was made to seem even better by Pinkie Pie's following commentary,"Here's your birthday cake, Dashie. Four layers made up of three different kinds of fudge, mixed with chocolate icing and plenty of cream on the inside. I hope you like it."

Like didn't begin to describe it. Rainbow Dash was practically drooling as she stared at the cake in front of her. It took all of her restraint to stop from simply shoveling hoof-fulls of it into her mouth. As soon as a plate was set in front of Rainbow she immediately put two large slices of cake on it and began going to work. Every bit of fudge that hit her tongue only made her more ravenous. Soon the first slice was gone, then another, and another. At first glance Dash thought she wouldn't of had a chance at taking on this cake alone, but she was already a quarter through it! It seemed that whenever she was close to getting full she somehow managed to find enough room to keep eating. Slice after slice found it's way down to her belly until very little remained of the once impressive cake.

Pinkie Pie looked at Rainbow Dash with awe, "Wow,Dashie. That's gotta be a record! I wonder if there's awards for this kind of thing!"

As much as Dash hated to admit it, her eating had been getting a lot more faster than her flying as of late. She still felt slightly pleased with herself,however.

"Wow,Rainbow. That was mighty impressive,"complimented Applejack as she walked over,"Ah was gonna ask if you'd join me and some other ponies for an eating competition, but it looks like you might of had yer fill already."

Dash didn't consider sitting out for a second,"Pffft. Are you kidding? I can totally keep going. There's no way I'm going to sit out of a competition, especially one I'm sure to win."As much as Rainbow was dissatisfied with how large her gut had become, it did come with a few perks. She heavily doubted that any of the other ponies at this party could even come close to eating more than she could.

Rainbow Dash followed Applejack to a line of tables stacked with all kinds of treats and moved to sit in the remaining open chair. The chair squeaked and groaned from Dash's weight as she sat down. Her plot squished outward and actually stuck out past the chair. Normally these type of wooden seats would be uncomfortable but her flank now had so much padding she hardly noticed.

She could barely contain herself as she waited for the start. A large stack of various flavored pies and mini-cakes directly in front of her. As the whistle blew signalling the start she immediately dove right in. She grabbed a pie in each hoof and consumed one in just a few strawberry filled bites. The other pie didn't last long either. It's blueberry wonder was quickly sent on it's way to Dash's belly. She didn't even bother to keep tabs on the progress of her opponents. She simply kept focused on absolutely destroying the pile of food in front of her. About half way through she started to slow down only to receive a second wind. Later she caught a third wind,a fourth, and so on. Soon all the food in front of her was gone. It wasn't until now that she realized she had won the contest a long time ago and had simply been gorging herself since then. The other guests cheered and clapped at her victory. Meanwhile, she simply laid back and rested a hoof on her rounded mid-section.

The party went on for the greater part of the afternoon before things started winding down. Aside from helping her experiment along, Twilight spent much of the time gauging the reaction of her friends to Rainbow Dash's changes. Applejack and Rarity seemed the most concerned about it, but both of them were too polite to say anything more than a passing comment or suggestion. Pinkie Pie seemed indifferent or almost amused by it all. Fluttershy,however, was difficult to read due to her shyness and withdrawn nature. All things considered, Twilight doubted that any of her friends would act enough to influence Rainbow Dash or the experiment.

As the party ended guests start slowing filing out. Twilight followed Rainbow Dash and the rest of her friends outside to say good-bye before parting ways for awhile.

"Thanks for the party,Pinkie,but I better be heading back home,"Said Dash as she turned and positioned herself for take off, unintentionally sticking out her large plot towards the group. A barely detectable "eep" came from Fluttershy,who appeared to be blushing as well. Rainbow managed to only get a foot or two of the ground before she collapsed. All the bulk on her body shook as she made contact with the earth. She wasn't going to give up easily though. Rainbow tried multiple times to take flight. However, no matter how hard she tried each attempt ended in her being pulled back down to the ground. Twilight also noted how Fluttershy seemed to be staring quite intensely at Dash's body and how she blushed deeper each time Rainbow's mass jiggled on falling to the ground."It seems I'm not the only one with some unique interests," Twilight mused to herself.

After about the fifth try Rainbow Dash simply laid on the ground and panted heavily. Her fur was now drenched with sweat from all the effort. A few moments later she slowly got up and looked at the ground with sadness,"I can't believe I let myself go this far."

Fluttershy quickly moved to comfort her,"Aw, don't get too upset,Rainbow Dash. I'm sure you'll work off a few pounds in no time and you'll be flying like normal again."

"Well,sure,"Rainbow Dash agreed,"But where am I supposed to stay in the meantime?"

Twilight wasted no time jumping on this new opportunity,"Don't worry about that,Rainbow. You can come stay with me until you get your flight back,and I'm sure Fluttershy can fly up to your house and get Tank for you,"Fluttershy nodded in response to Twilight's idea. To Rainbow Dash it probably sounded like a selfless offer. Twilight's motives ran quite deeper,however. She figured it would be much easier to conduct her experiment when the test subject was staying inside her own home. It may even open the door to push things further at a higher rate.

About a half hour later Twilight and Rainbow Dash arrived at Twilight's library. Rainbow Dash's first action was to lay down on the couch. She was clearly still depressed from the loss of her flight earlier. Twilight had to admit she was feeling a slight amount of guilt over it, but it was all only temporary. In about a month the experiment would be over and she could undo everything. Besides, she had already come too far to stop now.

"Thanks again for letting me stay,Twi. I'm sure it won't be for too long,"said Rainbow Dash.

"Think nothing of it,Rainbow. You can stay as long as you need. Now I'm going to make some dinner, you want anything?" Twilight offered.

"Nah, I think I've had enough food for today."

Twilight trotted into the kitchen, getting to work on assembling a large amount of hay burgers. Rainbow Dash might think she's had enough food, but there were ways to change her mind. From the privacy of the kitchen Twilight cast a quick spell to rejuvenate Dash's appetite. Sure enough, Rainbow Dash entered the kitchen not long afterwards.

"Hey Twi, I changed my mind. Think you can make me some of those burgers? I need a bit of comfort food right now."

Twilight smiled in response,"Sure thing,Dash. Coming right up."

Not long later a platter filled with nearly a dozen hay burgers was set down in front of Rainbow Dash in the living room,"You're a really great friend for doing all this,Twi,"Rainbow Dash said in gratitude,"Tomorrow I'm going to take my workout to the next level and show this belly who's boss. For now though, I'm just going to enjoy all this food."

Author's Note

I put effort into adding extra detail on this chapter, since many had advised me to slow the pace a little. Comments are welcome as always.