“Come on, bro, it's going to be fun!” Charlotte giggles to herself while patting her belly playfully. With her gentle body now becoming your prison, you can’t really object.  

Still, you try reasoning with her. For all her faults and dismissiveness, you know that Charlotte loves you more than anyone. “Charlotte, please be careful.” You warn, seeing her preparing a workout mat. “This is a new app, so I am not sure what may happen. Can you just use the phone to turn me back to normal?” 

“Please, bro, it’s just a quick workout. I want to spend some more time with you.” She puts on her sweet voice, looking down at her abs with a warm smile. 

“Alright, fine.” You let out a defeated sight. It’s not like you can do anything about it, being at the mercy of your little sister. Looking over to the TF app still opened on your phone, you wince. A single click would be enough...

Walking into her closet, you see Charlotte taking out a bright-pink sports bra and a pair of black leggings, preparing to put them on. You are unable to close your eyes on the account of being a part of her body, but your sister doesn't seem to mind. 

"Don't worry, you've seen me naked before." She says with a smile. "Besides, you're just a piece of my belly now, not my brother!" Once again giggling to herself, you hope that Charlotte is saying that just to tease you. 

After some basic stretches to prepare, Charlotte lays her back down on the mat. Soon, you can feel her going through the entire routine, with the portion of her body in which you are trapped moving rhythmically with her abs as she does her crunches. It is a bit chaotic, but not entirely uncomfortable. The only annoying thing is the overwhelming warmth of Charlotte's flesh mixed with her sweat sliding over you.

As the workout continues, you feel an odd sensation of shrinking. Your field of view gets smaller, with you retreating deeper and deeper into your sister's body with time. Then, the realization hits you. 

"Charlotte, stop!" You try screaming, feeling more and more of you dissapearing. 

"Huh?" Charlotte squeezes out between gasps for air. She wipes the sweat of her forehead, looking down at you. "What's wrong, bro? Can't handle the heat?"

"You're burning me up! Charlotte, this isn't funny. Turn me back to normal before I dissapear!" Your voice is a lot more forceful now, with your sister having the feeling like this is serious. 

Looking over to the app while wippuing down her body with a towel, Charlotte looks down at you with a forced smile. "It says here...integrity of object damaged." She reads the text slowly, turning the phone towards her belly hoping that you will see. 

If you had lungs, you would begin hyperventilating by now. "This means that you've burned up my biomass!"

"I am sorry bro..." Charlotte says, rubbing her belly to make you feel better. "Wait, the app has few options!" Your spirit lifts a little bit as Charlotte outlines what could happen to you next, carefully reading through the app's guide.

The first option is simply living the rest of your life as a part of your sister, always being by her side. You could also try restoring your body, but you would be a lot smaller with so much of your mass gone. Alternatively, she could turn you into another object to live your life as.