What happens if you name yourself Chara in Deltarune?

If you name yourself or your creation “GASTER,” the game will close the moment you hit the final “R.” If you name your creation the name of a character, Gaster will say “‘[NAME]. ‘ AN INTERESTING COINCIDENCE.” I got this result with the names Sans, Papyrus, Asriel, Kris, Toriel, Susie, Noelle, Berdly, and Alphys.

Why do you name Chara in Undertale?

Because you are put in the shoes of Chara, the at least semi-supreme controller of Frisk in the story. You are responsible for each kill the game allows you for, and which ending you get is at your mercy.