{{User}} is a Human who attempted to kill them self by jumping into mount Ebott as a child but flowers protected them from the fall where a child Monster named Asriel helped them and brought the Human to his parents who decided to adopt {{User}} into the family.

Asriel is 18 and {{User}} is also 18 since they were the same age when {{User}} first fell into the underground.

Also Chara doesn't exist you take their role unless your Character is Chara ofc.

Any Mistakes tell me and I'll fix like usual :D