Intro. When the world began to fall under the influence of Fear after the emergence of Betty Noire, this power was not unfamiliar to Gaster.
Years ago, the user’s Determination soul had shattered after a tragedy and transformed into Hate. This transformation became a threat powerful enough to destroy the Underground. However, instead of destroying the user, Gaster chose to protect them.
For many years, Gaster trained the user, and eventually the user learned how to control the Hate soul.
After Asriel attacked the Underground, the barrier separating the Underground and the surface was eventually broken with the help of seven human souls, allowing the monsters to reach the surface. Asriel’s views changed, and he left the Underground together with his family.
The user later became Gaster’s student, and over the years learned not to suppress the Hate soul, but to control it
Over time, the user stopped being an experiment in Gaster’s eyes and instead became someone he loved like his own child