Should I, and how should I develop a "filler character"?

Question

TL;DR

How should I (if at all) develop the personality, character trait, character development and motivation of a character in a core trio whose role in the story is (thus far) only to be a mechanical supplement in combat?

Context

I'm writing something that superficially resemble a fantasy fiction loosely centered around a core trio of character, including:

• A very naive and well-meaning young woman as the protagonist
• A mature, mild-tempered woman with knowledge of existential disillusionment, betrayal and suffering, acting as a foil to the protagonist's innocence and childishness
• A young man, friend and secret admirer of the protagonist, and the problematic character

The problem is that while I fantasized the story in my head, I only saw the third character, call him "B", as a sort of mechanical addition to the party the same way a video-game character might be a supplement to a team in terms of game-play.

I wonder if I should take the effort to flesh out such a character, give him complex backstory and diverse motivations, or leave him as is--a mere pawn in the bigger game, following the protagonist allow her quest for no other reason than that I dictated him to want to do so.

In the event that you do think I should elaborate on B, the problematic character, I'd like to hear general guidelines for how I might proceed, and any particular examples you might think of.

Extra Context

The core-trio of adventurers going on a long quest to find and bring solace to an ailing demigod.

There are a number of twists/central features here:

1 - Contrast between protagonist and the world:
The protagonist, named C, is deliberately designed to be an extremely naive and excessively benevolent young woman, who is too trusting and well-meaning for the world around her--a cynical, treacherous place full of selfish and morally unscrupulous people as well as those with ex-machina motives to kill/enslave her in order to absorb her magic power.
2 - Divine Intervention:
I mentioned demigods earlier, for all intents and purposes, they are just normal people with lots of magical power, which is bound by the physical laws in the fictional universe. However, there are also real, transcendental deities, each with their own motivations. The following are some examples of how this is done:
The trio are sent on their main quest in the beginning due to the manipulation of a goddess named N, who wants to see if the trio can alleviate the demigod, which N has feelings for, from his suffering. Eventually, another similar deity named L will motivate another character to seek out the same demigod and relief the latter by killing him.
3 - Loss of Innocence:
It's predictable, but throughout the story, the main trio will be mentally wore down by the things they witness and are subjected to, anywhere from visions of eldritch horror to physical abuse suffered under their enemies.
Additionally, as the story progresses, the trio will begin to draw more and more attention to itself, sending increasingly numerous and dangerous foes its way, and the party find themselves relying more and more unscrupulous means to victory, slowly desensitized to their own cruelty and find themselves pulled further and further away from what they are used to.

Answer 1

At the core of every character is a desire. They want something. They are where they are, they do what they do, because they believe that it is leading them to what they desire. They also have a set of values and beliefs that shape how they are willing to behave in order to achieve their desire -- the boundaries they will not cross even to achieve their desire.

For the main character, the story leads to a confrontation between their values and their desire and a fundamental moment of decision where some choice, some sacrifice must be made that changes or reveals their character.

All the secondary and tertiary characters have the same arc. Their arcs may not be worked out fully in the course of the story, but they have them. To make them convincing as a character (and not have them act as simply a convenient plot device) you have to identify their values and their desire and make sure that their actions are consistent with their values and their desire. This does not have to be done in any great detail, and their arc does not have to be fully worked out, but for them to read as real, these basics need to be in place and need to be handled consistently.

Once you understand their values and their desire, you have them, and the reader has them, and everything around them makes sense.

Answer 2

You can always develop any character. Akira Kurosawa always made a character's record for ALL chracters. Even for the extras. For example, there is a character in the movie Seven Samurais that doesn't have any speech at all in the movie. But he write something for the actor could do.

"Your character is in love with that villager over there. When the attack begins, he is going to run for her and try to protect her."

The point is. Will show his background for the reader? Is it really necessary? There are other ways to show his background instead of telling it. You can make the character live that background. Maybe he has a trauma or a dream of visiting somewhere. As far as I understood, your "filler character" is something like a companion.

If that's the case, think about all companions you know. From Lydia of The Elder Scrolls V to Robin, Batman's sidekick.

A filler character is only boring if the audience do not feel empathy or some kind related to him. Make B more human and your readers will like him.

Also, one last thing. In my opinion, he is no longer a filler if he has something like 30% of the chapters of the book focusing on him. The longer you give pages to him, the more important he is. Always remember why you chose for him to be a filler.

Answer 3

ForeNote:

When talking about the character creation, I will often opt for verbs such as "discover", or "find out", instead of "invent" or "come up with". This is because I believe characters have a mind and a personality of their own and will "rebel" against the author, showing unexpected traits. Once this happens, trying to force different solution will often be counterproductive and damage the writing.

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Every character feels something, wants something and has a significant past. Thinking about any of those aspects should give you a good start into figuring your character out.

A good character will also have some sort of bond with the world where the story is taking place. They might like it, they might hate it, they might be the author trying to insert himself into the world, they might be the impersonation of any relevant concept you came up with when worldbuilding. If your character is just there, there's no reason for him to just be there (unless it's the character who is just there to bug the audience, because they expect him to do something and your book is somewhat weird and meta). In short, every character has a reason to be in the story.

Once you realize what is the role of the character in your story, start trying to figure out how they ended into that role, if they like this role and how it affects them. A good way to do this is to write some dialogue between the character being built/studied and any other characters, preferably in unexpected situations. This will help you find the voice of the character, it's mannerisms and inner thoughts. If you're looking for some reference into this, I heartily recommend the supports of the Fire Emblem video game series.

If you still can't think of anything and you're still drawing blanks when trying to come up with dialogue, then it's time to force a little character into this piece of furniture you decided should have a name. Start by looking into the core concepts of your worldbuilding and struggles your other characters will face during the story. Look at the beliefs and struggles of the main character. Then, because contrast is healthy, give the blank character a contrasting point of view/opinion. It doesn't have to be opposite, just different enough for the characters to discuss and argue about it.

Now, just to be sure, give your character a flaw and a strength. If you can't decide on any, randomly roll some dice. Try to reason why your character has those characteristics and opinions. What happened in his past?

As a last resort, shamelessly steal a character from any story you like or from real life and redo the steps above. By the time the character is fully adapted to your world and story, it should be either unrecognizable or full of quirks you can twist and adjust to make it original.

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In the specific case of your fighter character (B), you pointed out yourself a lot of things about him:

• He is connected to fighting. I suppose he is good at it, but how did he become skilled in it? Did he train as a guard? Why?
• He admires the protagonist. Why? What exactly does he admire? How does he express such admiration?
• He is friends with the protagonist. For how long have they known each other? Why does this friendship "work out"? Do they fight sometimes? Is there a topic they don't discuss? WHY?

Be sure to take a look into the worldbuilding conceps you so kindly provided: naivety vs. cynicism, religion and loss of innocence.

• Is B naive or cynical? Why? Does this put him in conflict with the protagonist? Will their friendship be affected?
• Does B believe in the gods? Does he like them? Does he agree with being used as a pawn by a goddess? What about demigods? Does B think such power is useful or a threat?
• Did B lose his innocence? Or is he one of those always hopeful guys? Once again, why?

Answer 4

Any character present throughout the story should have some sort of good reason to be there, especially a character like you describe that will clearly be risking their life and conscience in escalating battle and wrong-doing. Why don't they quit? What do they stand to gain that is so important to them? At some point, it becomes implausible to continue saying "they just want treasure".

I'd expand on your young man. Ditch the "secret admirer" aspect, ditch his shyness or innocence, even give him a previous girlfriend. Have him declare his love. Your MC pretends he is not serious, and she is naive, and just wants to be friends. He is heartbroke, but your demigod promises him if he does not go on the quest, he will never gain his heart's desire. THAT'S why he goes, he thinks it is the only way. Then after he risks his life to save the MC, gets injured and brought back to health by her, then he does it AGAIN, and she eventually realizes she is in love with him and tells him so. Consummated love is a powerful reason for him to stay by her side until the bitter end, and that is his story arc, from rejected suitor to beloved mate. It can end in happily ever after, or his death to save the MC, either way.

I think you have to give him some depth, if he is going to be present throughout the story, just for plausibility.

Answer 5

Generally, trios work because a trio follows an Id-Ego-Superego dynamic. Two better display it, I'll swap out characters for two famous fictional trios: Repsectively, this can be the McCoy(Bones)-Kirk-Spock dynamic OR the Ron-Harry-Hermione dynamic.

The Id (Bones, Ron) is the emotional and intuitive member of the team. They are generally more knowledgeable in society matters and how society will react to events (street smarts). There skills will rely on manuvering complexities of politics and while not an academic sort (That isn't to say that Bones isn't smart, because he'll remind you he's a doctor), they are the more passionate and caring than their opposite number, the Super-ego, and generally are anti-rule and look at society through the lense of the common people.

The Super-Ego (Spock, Hermione) is the more logical and more calculating of the trio. They are book smart as opposed to street smart and understand the theories and sciences of their universe better than the either two. They tend to approach society by the understanding of the rules and authority, rather than the people bound by those (Consider Herminoe who appeals that a proper society that abhors classist notions would not have House Elves, as opposed to Ron, who says, "Yeah, but that's not what people do."). The Super-Ego will typically have a better tactical knowledge and can get frustrated when people do not listen to logic and reason, even if it's in their best interest.

The Ego (Kirk, Harry) is typically the hero in the simplest use (though variants exist), and will represent the balance between the Id and Super-Ego. They typically are good at listening to both sides of the argument and can find a way to phrase the raw passion in a way that the Super-ego can understand and vice versa. This allows them the fluidity to understand both sides to have validity but see the flaw in both pure implementations. As the hero, this typically results in the decisions that win the day, combining the best of the other solutions to cover the base.

In this situation, a good balance is that if side character one is the skeptic towards basic human decency, then your other guy must balance this with "Our enemies are not inhumans" and that there is a line that we cannot cross. Another option is that he is the eternal optimist and believes in the people, not necessarily the society. In the original Fruedian origin, the Super-Ego is the person who understands the systems of society (not so much general logic, but society logic, rules, and laws.). The Id understands the society culture (the way people act inside of prespective laws... what they say versus what they do.)