I adopted this idea from Firehedgehog, and who says that Frisk was the one with the Annoying Voice...

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Chara was sad... And they were angry... As they watched Frisk murder everyone in the Underground... Sans... Papyrus.. Mettaton... Dad... Mom... Everyone...

Thinking about their parents reminded Chara about the real reason why they didn't talk... It wasn't their fault that they had a voice that made everyone want to kill them! Wait.... Frisk could hear them.... And Frisk was the only one that could hear them...

Chara opened their mouth.

"I know a song that gets on everyone's nerves, and this is how it goes..."

They internally giggled when Frisk started to twitch...

----- Several Resets later -----

Sans watched as the Genocidal Child twitched, again... Before they started to yell.

"Goddamn it Chara! I'll stop killing everyone, and I'll Reset, if you shut the hell up!"

Sans blinked, and he stared at the ghost of the first human child, when they appeared, while everything was Resetting....

"There's a reason why I don't talk..." Chara told him, and Sans winced, when they heard their voice... And then, he grinned...

"Kid... I'll give you more annoying songs, to use on Frisk, if you promise to do this again, if they start killing again."

Chara had a huge grin on their face. "You have a deal, Sansy..."

Sans smiled... He had quickly learned how to tune out the annoying part of Chara's voice...

Chara wasn't the only one that had an annoying voice, but in Sans's case, puberty had fixed that... But Chara had died before that could kick in...

Sans smiled. "If I was a kid... I might have done the same thing to make Frisk stop."

"Do you wanna be 'Annoying Voices' friends?" Chara asked him.

"Yeah... Let's be 'Annoying Voices' friends." Sans smiled, and he highfived Chara, right as the Reset kicked in, and a new Timeline was started..

-----

Frisk breathed a sigh of relief, when they woke up... Chara, and their annoying voice, was gone... They hummed, and they started to walk out of the room with the golden flowers....

Chara silently chuckled, as they followed Frisk... This was going to be fun...