er, dont ask.
anyway, just inc ase you forgot'ill repsot my suggestion
okay, here's my suggestion for your kaijin.
Do you know of Personal Demons in psychology?
Personal Devils
Their orgin is ambigiuous, however, it is clear that they are a threat to humanity.
They have no definite form.Their form is mainly based on the emotion the human mainly experiences and exhibits.Mainly, they are invisible to normal humans.
The emotions are fear, doubt, worry, shame, guilt and rage.Mainly negative emotions.
They prey on mainly humans with lots of those emotions.
Attacking method
When they manage to get to a human, they will stay inside their mind.They will influence the human, into experiencing more of the negative emotions,until, when they have eaten enough of the negative emotions, they will be able to jump out of the human and manifest in physical form.
Mainly, after manifesting, they can choose kill the human afterwards.