It is not ethical at all. Teachers are in the position of guiding and educating students. Forcing them to create a so - called 'fantasy story' in an improper way undermines the relationship between teachers and students. Moreover, it may also go against the school's code of conduct and educational values. In a proper educational setting, interactions should be based on mutual respect and positive communication.
No, it is completely unethical. Teachers are professionals and should not be forced to do something against their will or professional ethics. Forcing them in such a way violates their rights and the respect due to their position in the educational system.