Enter Shortszilla! (fan story)
(This story is NOT CANON to Pantszilla!)

A chubby blue crocodile arrived at the ruins of the old lab. The old lab where his best friend was kept. Where he found the safe keeping the chemicals that made him grow and cause his pants to swell inside. The crocodile remembered how he helped him escape from his cell. He remembered how he escaped and watched his friend go wild on the city as the kaiju, Pantszilla.
       And then, Pantszilla conquered the Earth by stuffing it into his pants. The crocodile looked up at the orange sky. He felt so much envy for him. He wanted to be a big kaiju, just like him. And even more, he missed his best buddy and wanted to be with him. The crocodile looked down at the ruins of the lab and hurried, preparing to start digging.
  "I wanna be like you, bud.." He said to himself as he dug with his claws through the dirt and rubble. It felt like he searched for hours, until finally...he found it. The safe that the formula was kept in. "Yes! This is it!" He said happily. He quickly opened the safe and found two vials. One contained red liquid while the other had green liquid inside.
  "It's still here!" He whispered. Without hesitating, the crocodile picked up the vials. "I hope this works. No going back." The crocodile said to himself. He poured the red vial all over his body and pants, then sat down on a large rock, pouring the green vial entirely on his orange pants. The crocodile sat there and waited for the effects to kick in. And soon enough, they did.
      The crocodile suddenly heard a hissing noise. His bright orange pants began to grow wider and puffier and even started to become more round. "Rampaging reptiles...it's working!" He laughed. He felt bigger and lighter and even felt himself starting to grow a bit taller. "C'mon, baby! Make me bigger! C'mon!" The crocodile cried with excitement. His tail thumped against his big, round pants that were growing larger and rounder by the second. The butt of his pants had grown to the size of a big balloon!
     SHWOOMP!
Before the crocodile knew it, he grew to the size of a kaiju. He was practically 50 feet tall! The crocodile let out a happy roar and gave his butt a slap. "I AM SHORTSZILLA, FRIEND OF PANTSZILLA!!" He roared with happiness. Shortszilla then stomped over to the city. He heard screams of panic as he looked down and saw tiny civilians running away from him. "Not another one!" Someone yelled. He looked down to see an industrial pillow factory, as well as kaiju-sized pillows.
        He saw an iguana shaking his head. "A factory error?! What are we supposed to do with kaiju sized pillows?!" The iguana shouted angrily. Shortszilla looked down at his inflating butt that was already the size of yoga balls, at least in his eyes, and giggled. "Maybe I can help!" His voice boomed. He tore off the roof of the factory and picked up a pillow. "Mm..such soft cotton!" Shortszilla chuckled. Then, he grabbed the waistband of his pants and opened them wide, stuffing the pillow inside. Once it was completely stuffed in, he snapped his waistband shut.
     The stuffing felt so good to Shortszilla, and he soon felt his size increasing and his pants start to inflate even more. "I'm getting even BIGGER!!" He cried, happily. The iguana quickly panicked and ran away from the factory. Shortszilla didn't stop there. He stuffed pillow after pillow after pillow, watching him and his pants grow and grow the more he stuffed. By the time there were no more kaiju-sized pillows, he was almost 100 feet tall!
Shortszilla rubbed his massive butt with pure joy. "Gotta get bigger! I don't wanna stop!" Shortszilla then laughed and without hesistating, he turned around and sat on the now tiny pillow factory, feeling his giant, heavy butt smush everything. He grinded and bounced against it a bit. Standing up, he found that the pillow factory had been crushed all to rubble.

"Hmm..what else can I stuff.." He said, looking around. Shortszilla suddenly spotted what looked like a big storage warehouse. He waddled over to the warehouse, his massive, heavy butt bouncing. As he moved, he could feel the pillows in his pants bouncing and moving around. Shortszilla giggled and rubbed his pillow stuffed pants. "Hehe..so fluffy.."
Shortszilla then moved towards the warehouse. "Wonder what's in here.." Shortszilla spoke as he tore off the roof, finding a bunch of balloons inside, from parade balloons to even a blimp. They were all fully inflated, but were never moved out because of Pantszilla stuffing the Kaiju balloons down his pants, and so the parade was called off, and these balloons and this blimp was left inside.
"Now THAT'S what I'm talking about!" Shortszilla laughed. He picked up a giant parade balloon that looked like a red dinosaur. He open his pants wide and began to stuff the balloon into his pants. "Sorry buddy..but it's time for you to join your ancestors!" Shortszilla laughed.

Shortszilla felt pure happiness as the balloon went into his pants. He let out a big, happy roar, letting go of his waistband, and feeling it snap shut. He felt his massive pants growing and inflating even bigger and felt his height increasing even more. Shortszilla kept going, stuffing balloons into his pants and even stuffing the blimp into his pants. He let out a massive roar as he grew and grew. Shortszilla saw the far distances of the earth and the city under him getting squished and squashed under his pants. He suddenly felt himself start to rise off the surface of the planet.

"This is awesome! I've outgrown the Earth!" Shortszilla saw the earth below him, seeing how much smaller it was now. 
Then something caught his eye. Something green and scalie like a lizard's skin. It looked like Pantszilla's legs dangling about. "Hehe..just wait until he sees me." Shortszilla laughed. Shortszilla grabbed onto Pantszilla's legs to get his attention and began to climb up to the waistband. When he got to the waistband, he used his hands to push it open and he began to push himself through until his head popped out of the waistband. He saw nothing around him but space and stars. And of course, his best friend's oversized pants and body.

"No way...is that you, buddy?" He heard a voice.
Shortszilla looked up to see Pantszilla looking down at him, smiling. He reached down and opend his pants, pulling Shortszilla out of his pants. As he did this, his pants and Shortszilla's pants made squeaks. It was a bit of a struggle to pull him out due to Shortszilla's massive inflated pants. Shortszilla was the size of a bowling ball compared to him. "Yeah..it's me, heh.." Shortszilla laughed. Pantszilla smiled and hugged his best buddy close to him. It felt like he was hugging a big, fat balloon! Shortszilla returned the hug, resting his head on his shoulder. "Oh my god..feels like I haven't seen you in forever!" He laughed.

Pantszilla then held him in front of his face. "And your pants! How did you grow like me?" He asked. "I wanted to be like you..being a kaiju must be so awesome. So I went to the old lab and found those vials and..well, yeah heh."
Pantszilla laughed and patted his best friend's head. "That is awesome!" He cried. He gave his pants a few squeezes, feeling the balloons and pillows inside. "You'll make a great kaiju...eh, what do I call you now?"
Shortszilla chuckled a bit. "How about Shortszilla?"
"Yeah!" Pantszilla roared. "It's you and me now! Pantszilla and Shortszilla! And we're gonna stuff everything in our pants!"
To be continued...?