Board Thread:General Discussion/@comment-26006155-20160613103837/@comment-27089028-20160628193541

It Perished alongside Asriel's after he was killed but was subsequently revived inside of Flowey where Chara's negative energy unconsciously influenced Asriel's Soul inside Flowey thus explaining the lack of compassion or positive emotions altogether. The Reset power also originated from Chara's souls which is why when Chara's soul found a more compatible host in Frisk the Reset power was transferred over to Frisk as well.

In the Genocide Route Chara begins to stir and Frisk's own negative energy brings out the worst in Chara who's eventually grows powerful enough to take pilot over Frisk's body.

In the Pacifist route, the good side of Chara is allowed to shine and it's his memories and his influence that allows Frisk to reach Asriel ultimately giving us the True Pacifist ending.