'The brain...is not a veteran demon...' Lucifer thought as he realized this.
Right, it is the truth that the brain is not a veteran demon or anything of the sort.
After all, he is just a brain. Although there are monsters or demons who are missing some body parts, they are still capable of fighting.
The brain...is not capable of fighting since...he just does not have a body or anything of the sort.
Of course, there are several ways for one to be recognized as a veteran demon. It is not only by fighting that one can become a veteran demon.
One can also become a veteran demon if one practices his will, mind, and determination.
If one has extraordinary willpower and mental focus, then one could be considered to be a veteran demon.
However, one would have to go through many tribulations, hardships, and ordeals to even have the extraordinary willpower one would need to be recognized as a veteran demon.