@VilVil
Makima is a devil, not a fiend. Unlike devils, fiends only have a fraction of their original power, cannot make contracts, and their head is transformed to reflect part of their original appearance. When they possess a human body, it is
already dead. Makima and other pure devils don't use hosts per se; their bodies are their own, and they can form contracts and use all of their power at will.
Devilmen—devil-human hybrids like Denji and Makima's squad from this chapter—are the exception to this, as they do use a host but retain all or most of their hosts' original human faculties and appearance (presumably due to fusing with still-alive hosts via a contract) while being able to transform and use their full devil power at will. They're technically a far superior version of fiends.