It does
Everyone has Battle Spirit as confirmed by Akaza. Battle Spirit is indexed as Chi in vs battles. The only way to remove Fighting Spirit is to go into
Selfless State.
This is just flat out wrong and demonstrably false. With what empirical evidence did you use to come to that conclusion? Enmu has
Sleep Manipulation, Doma has
Ice Manipulation, Emotion Clones can use
Sound Manipulation,
Lightning Strikes,
Air Manipulation, and
Wood Manipulation. A
low tier demon literally has
Vector Manipulation.
Battle Spirit is shown to effect other people without the use of biological or cellular manipulations. Zohakuten
looked at Tanjiro and induced fear into him. Kokushibo did the same thing to Muichiro and Yoriichi to Kokushibo.
Those three examples of Fear Manipulation had nothing to do with manipulating biology or body chemicals to cause fear, and it wasn't described as such. You are confusing the results of the
Fear Manipulation with the method of how it works.
Battle Spirit is NOT manipulating a person's biology and brain chemicals to be scare them.
Battle Spirit is scaring a person using
Chi and
Aura and that fear causes the person's body to experience multiple negative effects (shaking, shuddering, heart stopping, etc). Whatever happens afterward is the product of that fear, but the fact remains is that the person is scared.
Just because BoBoiBoy doesn't have organic parts doesn't mean he wouldn't be scared, it just means his heart will keep beating and he wouldn't be shuddering. He'll still get scared because of the
Fear Manipulation and he will be unable to move because of that fear. The
Paralysis Inducement is a package deal that comes with the
Fear Manipulation.