According to Greerwu's account, its adolescent appearance is referred to as an immature form.
It is the primary state of a Pattern Demon.
Once a young fire demon matures and transforms into a Pattern Demon, the amount of energy required to sustain its true form becomes unsustainable for a newly matured Pattern Demon. Consequently, the vast majority of Pattern Demons initiate their immature state to consume less energy.
Only when their power increases in the future and their energy reserves are sufficient will this juvenile state slowly vanish among the Pattern Demons.
It does sound similar to the concept of energy conservation in Mechanical Alchemy.
Once the low-energy mode is activated, the loss of one's energy will be minimized.
Angel felt somewhat sentimental; although demons have not developed a special knowledge structure, many concepts in their philosophy of survival actually fill the missing link. Take, for example, this typical "laying low and biding time" mode.