One night Kyousuke Date walks into his house and finds his mother dying in a pool of blood. In her final moments, she stabs him in the chest. After a quick recovery, Kyousuke is determined to unravel the mystery behind his mother's actions, but his search leads him to be attacked by two opposing groups, the Hospital and the Kirihara Group. As Kyousuke fights to survive, he discovers something unbelievable - he has a twin sister named Runa, unknown to him until now. Both groups relentlessly pursue him for information about her, but Kyousuke is clueless about her existence. With no other options, Kyousuke turns to his incredible new power - the ability to transform into a monstrous mutant known as SoulTaker. He sets out to crush both organizations, find out the truth about his mother's actions, and protect his newfound sister Runa.