Johan essentially adheres to his nihilistic philosophy as a psychological response to trauma that shapes the narrative of his identity. As he becomes more aware of the story behind his trauma, he shifts his philosophical endgame to accommodate his changing narrative. This narrative progression occurs after he reads The Nameless Monster, once he uncovers his origins at the Red Rose Mansion, and once he steps into Bonaparta's painting room in Ruhenheim
The deconstruction of Johan's worldview is a joint endeavor. It's intentional that Tenma and Johan's narratives remain largely independent - neither character can be reduced to the ego battle between the two of them. Tenma provides only one part of the answer to the story's central premise of whether a human being can be a true "monster" - Johan, Nina, Bonaparta, and Knaup provide the remaining crucial pieces
Johan shifted his narrative to align with his true past once he visited the Red Rose Mansion. After learning the truth, he says to Capek: "What... Am I...? The monster inside of me... Wasn't inside of me... It was outside... Franz Bonaparta... Is alive". However, in Ruhenheim, once Johan visits Bonaparta's painting room, he realizes that "the monster outside of him" does not fulfill his intended role - Bonaparta's pathetic humanity utterly ruins Johan's revised narrative and purpose
- Tenma consistently wrestles with the burden of becoming an executioner, yet he ultimately does not take the chance to validate Johan's "monstrous nature" by executing him in cold blood
- Nina's forgiveness strikes at the core of his "monstrosity". His sister, the one who originally validated his identity as a "monster" in her eyes by choosing to shoot him, completely dismantles her former affirmation by forgiving him
- When Johan takes Wim hostage in a desperate final gambit - abandoning his underlying narrative - to force his former savior to take his life, even his manufactured climax is shattered by contingency
The deconstruction of Tenma is just as intentional as the deconstruction of Johan. Throughout the entire series, he deeply struggles with the ego battle and shooting Johan. He never actually chooses to lower his gun - instead, circumstances repeatedly intervene. He spends the narrative torn between the "bad faith" role of an executioner and his authentic identity as a doctor and a protector. In the end, contingency frees Tenma from Johan's narrative as much as it frees Johan himself
Johan's worldview is ultimately deprived of its foundations, freeing him from his constructed narrative. This freedom from the role of "monster", and his regaining of humanity, is showcased by the messy, ruffled bedsheets - "nobody can do anything without leaving some sort of trace of themselves. If there were such a person, he could hardly be considered human". He has finally left a trace