Damn It, My Whole Family Is Full of Monsters

The world has descended into madness, and extreme emotions have become a breeding ground for monsters. I lost my memory before I was eight years old, and I tried to find clues to find myself, but to no avail. I thought my future life would be uneventful, until that night, a little boy who claimed to be my brother came to me... He merged with me and tore apart humans mutated by extreme emotions. But my 'brother' is too evil. He is so evil that he looks like a real monster. However, he told me that there was more than one family member like him. "My parents are on their way. They... Miss you more than I do." ... Later I realized that when the world falls into madness, the only ones who can fight against the monsters are my more evil family members in the house.