>>32972061>TotTLet's break it down. Fear is in its purest form, a state of mind. It's universal, and therefore can be communicated in one's writing by speaking to the mental instinct(s) we all share at some level as living creatures. This is the basic idea of instinctive fear, tied not to reason, but lack thereof. An absence of reason or inability to exercise sound judgment gives rise to emotions such as irrational fears. Fear can also be existential, pertaining to one's place in the universe. Finally fear can be natural, the fear of freezing to death, not finding shelter or the like. Often fear is tied to stress and obstacles, however that is not a comprehensive definition.
In a way this makes fear a very important, albeit intangible, member of a story's cast. Without it, the characters are incomplete. If personalities lack fears, they are difficult if not impossible to relate to. I'm a fan of splitting fears into two degrees. First, there are the personal fears. That's subjective, and the existentialism mentioned falls under that umbrella. It also includes compulsive fears. Such can come in many unique varieties, perhaps in the form of a strong revulsion to a certain species and type, or maybe a fear of heights for example. This general fear builds the character by giving them some internal adversary because, news flash, we all have those. Secondly, I build natural and primal fears. These concern the struggle to survive a harsh world amid truly bizarre creatures, while facing the paranormal and unforeseeable entities present in a fantasy world such as Pokémon.
As for what makes it believable: it is the twofold types of fear already articulated having demonstrated influence on the characters. Simply stated, it is showing their effect. The natural fear and the personal fear duet work in tandem to keep a story from becoming too stale or biographical, however the ultimate goal is to make the characters believable through their believable fears.