Chara (pronounced KARE-uh) is the main antagonist for the Genocide Route of Undertale.
Not much is known about Chara before s/he fell into the Underground, but it is known that s/he hated both Humans and Monsters. It is also implied that Chara attempted suicide on Mt. Ebott by jumping down the hole. As soon as s/he woke up, s/he met Asriel. He took Chara to his parents' house, where s/he was instantly adopted. At some point, Chara hatched a plan with Asriel to break The Barrier and destroy all the Humans. Chara consumed buttercup flowers to make her/him deathly ill. S/he died, and her/his SOUL persisted (as Human SOULs do). Asriel, fulfilling Chara's plan, absorbed the SOUL and passed through The Barrier. Unfortunately for Chara, Asriel decided to resist her/his commands and sacrificed his life to keep the Humans alive.
During the Genocide Route, as Frisk is slaughtering all Monsters and gaining LV, Chara's mind slowly starts taking over Frisk's body. We know that Chara is talking to Frisk when the textbox's text turns red when selecting an option or checking an object. Chara fully takes over Frisk during the fight against Sans in the infamous Judgement Hall. After s/he finally ends the life of Sans, s/he goes into Asgore's castle and kills both him and Flowey. After that, Chara gains a physical form and asks Frisk to rule over the world through more genocide. If Frisk says no, Chara tells her/him that s/he was never in control and then causes over 9,999,999 attack damage to the entire universe. Frisk can contact Chara to restart the world, but it costs Frisk's SOUL.
- Human Physiology - As a Human, Chara is way stronger than a Monster (as one Human SOUL is equivalent to all the Monster SOULs).
- Determination Manipulation - With Determination, Chara is able to reverse time, resurrect herself, and boost her strength.
- Universe Manipulation - At the end of the Genocide Route, Chara instantly destroys the universe with one hit. If a certain goal is met afterwards, Chara will then recreate the universe perfectly (in exchange for Frisk's SOUL, which may mean that this ability comes from two Human SOULs).
- Possession - It is heavily implied that, throughout the Genocide Route, Chara is controlling Frisk through possession.
Chara can only be resurrected if all the Monsters in the Underground (except for Alphys, the Amalgamations and Napstablook) are slain. She also needs her vessel to gain an LV of 20 before she has enough power to become physical.
- Chara design is based on Frisk, another Undertale character, but there are multiple differences.
- Chara's hair is a lighter brown than Frisk's.
- Chara's shirt features a green base and a big, yellow stripe, while Frisk's shirt has a blue base and two small, purple stripes. Her pants are brown instead of blue.
- Chara's face is quite different. Her eyes are wide open, unlike Frisk's. She has a grin rather than Frisk's expressionless face. Her skin tone is lighter than Frisk's. Finally, her cheeks are shown to be pink, whilst Frisk's cheeks aren't shown at all.
- The name Chara is derived from "character", leading many to believe that her name is pronounced "KARE-uh" rather than "CHAR-uh".