Love gone wrong can lead to it too. In a tragic love story, a man who was spurned by a powerful witch or enchantress might be turned into a statue out of her anger or heartbreak. His immobility would be a representation of the end of their relationship and his fate sealed in a cold, unchanging form.
Betrayal could also be a cause. In some fictional tales, if a man betrayed his comrades or a powerful entity, that entity might use magic to turn him into a statue. It's a way of imprisoning him in a form that can't interact with the world anymore. For example, if a knight betrayed his king and made a pact with the enemy, the king's wizard could turn him into a statue.
One famous example is the story of Narcissus in Greek mythology. He was so in love with his own reflection that he couldn't leave it. Eventually, he turned into a flower, which could be considered a form of becoming a 'fixed' or statue - like entity. Another could be from some local folktales where a man who was cursed for his pride or disobedience to the gods was turned into a stone statue as a form of punishment.
It could be a scientific experiment. Scientists might be testing a new technology or drug that has unforeseen side effects, causing the transformation. This could then lead to a story about Otto Rocket trying to reverse the process while dealing with the new experiences of being a girl.
One reason could be a curse. Maybe she offended a powerful witch or magician, and as a punishment, she was turned into a mannequin. Another reason might be a deal with the devil - like figure. She made a Faustian bargain and the price was her transformation.
In some stories, it could be the result of a curse. Maybe the person has done something immoral or broken an important taboo in their society or a sacred place. The curse then takes effect and changes them into a cock as a form of divine or karmic punishment.
One possible reason could be a magical or supernatural curse. Maybe he offended a powerful witch or wizard who cast a spell on him. Another reason could be some sort of scientific experiment gone wrong. For example, if he was part of a secret experiment involving hormones or genetic manipulation, and things didn't go as planned.
Maybe it's a case of urban legend or a tall tale that got out of hand. People love to tell extraordinary stories, and if there was someone with an unusual appearance due to a medical condition, it could have been embellished over time into this idea of a man turning into a walrus. Also, lack of medical knowledge in the past might have contributed to such wild interpretations.
It could be a result of a scientific experiment gone wrong. In the Star Fox universe, if there are advanced scientific experiments happening, something could have malfunctioned. Maybe a new form of energy or technology was being tested, and Krystal was in the wrong place at the wrong time. The energy could have had an unexpected reaction with her unique physiology, turning her into a stone - like state.
In some turned into a girl stories, it could be due to a curse. For example, if someone offended an old witch or a powerful spirit, they might be cursed to change into a girl. Also, there could be a strange natural phenomenon. Like in a place full of strange energy, a person could be transformed into a girl just by being there for a while.
One possible reason could be a magical curse. In many fictional tales, a spell might be cast on the husband, perhaps by an angry witch or wizard, which changes his gender. For example, in some fantasy stories, if the husband unknowingly offends a magical being while trespassing in a forbidden forest, this could be the result.
It could be due to character flaws or bad choices they make. Maybe they are lured by money or fame in a fictional setting.