It donned on you that Toriel knew Chara. She was her mother for a few years before Chara's death.

"How are we going to keep Chara under the radar? I mean we can't have Toriel noticing her!" You said. Chara turned and looked you, her smokey trail following her form.

"I could either keep hiding and follow you, which is risky, or fuse with one of you," she said.

"So it's either don't fuse and possibly get caught or fuse and get out together," you said to yourself. Frisk spoke up.

"I can fuse with Chara!" They said. You looked at the child, beaming and filled with determination!

"Okay then...go ahead," you said, motioning for the process. You knew Chara was a mostly physical being, this meaning if she his, it'd be slightly harder to do that it was before. Fusion was the best option. You remembered reading up on the topic in your third timeline.

"Ready, Frisk?" Chara asked.

"As ready as ever!" Frisk said. You watched as the two started a dance. Smooth movements on both parts.

A flash of light blinded you for a second before the figure emerged. It looked like Frisk, just with red eyes and brighter colored hair. You figured as much, knowing the two looked fairly similar.

"Ready guys...er...what do I even call you?" You asked.

"Charisk. Just keep it as Frisk around Toriel, though," they said.

"Okay then. Off we go!" You said, walking out. You and Charisk abandoned the toy knife.

It's short I'm sorry! But I just had the idea and I can't come up with anything else...sorry