You should use a TWeakObjectPtr<ACharacter> to hold the weak character reference in your code.
Is it specifically designed for this sort of thing:
/***
*
* FWeakObjectPtr is a weak pointer to a UObject.
* It can return nullptr later if the object is garbage collected.
* It has no impact on if the object is garbage collected or not.
* It can't be directly used across a network.
*
* Most often it is used when you explicitly do NOT want to prevent something from being garbage collected.
**/