Asriel struggled himself into a seated position, looking down in shock at his stomach. It hissed as he found himself swelling up, his shirt becoming tight and riding up. He clutched his stomach in pain.
"Chara! What's happening?"
Before long, his butt began to inflate as well, the magic moving around his whole body and turning him into a ballooned-up version of himself.
Chara could only look on in wonder as her brother inflated, poking his swollen stomach teasingly.
"You're blowing up, Asriel!"
The goat took a good look around his body, his belly having inflated to a round ball on his tiny frame, his arms and legs thickening, his fingers and toes becoming bloated and useless. He noted that as parts of his body started to expand, the pain reduced, and he was left with a very tight feeling on his whole body.
"Wh-what do I do?" The fear seems to have subsided, but his voice was raised in pitch. Chara chortled.
"I-I don't know." She giggled a little bit at how silly Azzy sounded. "You sound like a helium balloon, though."
Azzy blushed, and yelled in the same helium-imbued voice. "Go find out what you did!"
"I know what I did, silly." Chara smiled. "I made you a balloon."
The child's body creaked, his elbows and knees being forced straight as they too filled with the magical gas. "What?? Why?"
She giggled. "I thought you'd look cute. And you do!"
Asriel exhaled through his snout, his attempts at pouting foiled by his swollen chest.
Chara bounced over to her brother, planting a kiss on his nose. She put her hands on Asriel's soft, bouncy shoulders, pushing him around and watching in glee as he sprung back, like a rubbery doll.
"C-can you put me back, Chara?"
Chara gave it a think for a little while, gazing upon Asriel's frame. Every part of his body had expanded aside from his chest down, his torso a single airship-shaped balloon, his arms and legs spread out and swollen. His clothes no longer fit, his pants snug on his legs like sausage casings and his shirt hanging underneath his armpits, fully displaying Asriel's expanded, hapless body. Any more pressure, and they'd both tear right off, not like there was any getting him out of them without deflating him. She really did like him like this; big, round, and completely at her mercy.
She decided...