I'm working on a weird fantasy novel involving the theme of "identity" and I'm looking for advice on ideas or themes. The protagonists were a pair of vat-born slaves who were genetically conditioned for mercenary work, for example, and their arcs involve them attempting to reject the roles they were built for and become free. Another idea I had was for a monster that only exists because it believes in its own existence, and the heroes defeat it by convincing it that it isn't real, which causes it to cease existing.