After Eating Little Red Riding Hood, the Wolf Discovered the Truth

Fangs, Claws, Scales, Alien Eyes, Long Horns, Tentacles 😫

The best thing is that the protagonist gradually changes/grows these structures in human society. The second best thing is that the protagonist himself already has this kind of body structure /////////It is also okay to directly travel to the demon clan and devil king in a different world /////////Replace the san protagonist