Basically, someone who can RESET and the literal devil of Undertale vs. someone that can manipulate time. Chara has the Real Knife and The Locket. Frisk has the Worn Dagger and Heart Locket. Time Eater is controlled by the two Eggmans, like the Sonic Generations boss fight. Who would win. (Note, this is based on the boss fight with the Time Eater in Sonic Generations, and Frisk can sell their soul to Chara, so they're both fighting Time Eater, just at different times)