(chara is female here sorry :p)
SURFACE
12:00 A.M.
Chara opened the door to Asriel's room and crept inside. The monster was snoring loudly—she knew she couldn't wake him unless she made the loudest sound ever. She walked through the dark until she reached his nightstand. She reached up and grabbed something smooth and rectangular. "Great, I found it!" she whispered. Holding the object tightly in her hands, she snuck around his bed and made her way out the door.
She tore another cube off of the object she had found on her brother's table. She placed it in her mouth and started to chew. The chocolate was delicious and sweet. Asriel would never find out if she was sneaky. She finished the last section of the candy. Now she just had to make sure that Asriel thought his sweet treat was still beside him. She grabbed an old strip of cardboard from a school project off of her desk. She carefully placed the strip inside of the wrapper, and taped the wrapper back into place. She carefully made her way into his room again and placed the "chocolate bar" back where she had found it.
THE NEXT MORNING
Chara laughed as Asriel screamed from inside his room. He burst out the door and stomped over to her. "Chara, you ate my chocolate, didn't you?!" He hissed. "What chocolate?" She asked innocently. "YOU KNOW WHAT CHOCOLATE!" He shouted. Chara giggled. "I only saw some cardboard!" Asriel growled. "You'll give me the next chocolate bar you get." He said and walked off. "I definitely will," she whispered to herself when he was gone. "And then I'll steal it back."