Before I start, I'd just like to clear up that I think of Frisk as a BOY but Chara as a GIRL. I know it might not make sense but it'll be easier for me to write them that way.
Frisk stood patiently in the black void, really wishing there had been a better way to do this. A code word? Some polite message telling her he wanted a better deal? Nope, he had to kill everyone and destroy the world. Just to have a chat with someone he didn't even like.
As if on cue, he heard Chara's chuckle behind him. He sighed and turned to face her. She grinned. "You're confusing, you know?" she noted. "I thought you said you weren't going to do this again, but here you are." He scowled. "You know why I'm here." "Oh, I do?" she teased. "Give me my SOUL back, you genocidal maniac!" Frisk roared. Chara smirked. "I need something, though. Remember, You're not exactly in a position to negotiate. Hmm... If you're really wanting your SOUL back, I suppose you could let me take someone else's... I'm sure they wouldn't mind." she laughed cruelly. "I'm feeling poetic for once. Say, if I can't have yours, I suppose I could have the SOUL of the one who loves you most?"
Frisk thought this over. The one who loved him most? Wouldn't that be Toriel? She literally couldn't imagine him doing anything wrong... He really wanted his SOUL back, but would it be worth it? He sighed again. "There's a catch. There's always a catch." he muttered. Chara put on an obviously-faked look of disappointment. "Aww.. It's much more fun when I don't have to tell the catch! I'm thinking... maybe some of those golden flowers that grow in the Ruins. I'm taking those." Frisk was relieved.
"Just flowers?"
"Flowers and the SOUL of the one that loves you most."
"Yeah, well, the catch is just the flowers?"
"Yes. Those flowers. They're... they're uh, pretty."
"Deal."
Chara grinned. A sudden flash of light made Frisk flinch, and he suddenly found himself with nothing underneath him. He was falling. Only catching a glimpse of the Ruins below him, he saw the bed of flowers that had softened his fall originally were almost entirely gone... There was a horrible crunch as a flash of pain seared through his entire body. As his vision faded to black, he cursed quietly. "D-damn you, Chara..."
Hehe. Damn you, Chara... Oh, well. So anyway, this is The Price Of The World, and it's going to become one of my main stories. Enjoy!