Need is an aspect of the world our characters inhabit.
The props we place in the setting our characters inhabit, the tools they use, the objects they must acquire – these things form a layer that grows out of need.
First, no matter what genre you are writing in, you must establish the level of technology. Whatever you do, don’t stray from it
The Romans had running water, central heating, and toilets in their homes. So did the Minoans. However modern-seeming their architectural creations were, they were low-tech.
In the environment of any genre, cups will be cups, bowls will be bowls. The materials they are made of might be different, but those items will always be needed. If you took a Minoan and transplanted them into modern-day Seattle, a bowl or cup would be instantly recognizable for what it is.
Furnishings will be similar from society to society—people need somewhere to sit or sleep, whether it is a pile of straw, cushions, or a bunk. They need a place to cook and somewhere to store preserved food:
- A fire pit and baskets in a hut
- A fireplace and shelves with baskets and clay jars in a cabin
- A modern kitchen and pantry in a ranch house
- A starship’s galley or food replicator
Settings are like Barbie clothes. The clothes of Soldier Barbie fit Corporate Barbie… and Malibu Barbie… and Star Wars Barbie. The outer garments might be changed for each genre but Barbie is still the protagonist.
We change settings to fit the genre, to create a setting with all the right tropes. Genre defines the visuals, but the characters are paper dolls we dress to fit the society we have placed them in.
You can take your protagonist and place them in one of three kinds of settings: fantasy, sci-fi, or contemporary, and they would still be who they are. In any setting, there are certain commonalities with only minor literary differences.
Take a soldier as an example. They need garments, weapons, armor, and sustenance. Those are tailored to fit your genre—sci-fi, fantasy, or contemporary military thriller. But you can also use those things to offer visual clues about your protagonist’s personality.
Whether the weapon is a rifle, a sword, or a phaser is dependent on the level of technology you have established.
Logic and the established level of technology determines how each need is met. In the case of weapons, you’ll find many varieties of each within each category.
Which kind of hand-held weapon your protagonist will use is dependent on their skill level and physical strength as well as what is stocked in the armory.
When it comes to weaponry, if you are writing about them, you need to research them to know what is logically possible. Within each genre, one thread remains the same: strength and skill are determining factors when it comes to weapons.
A cutlass is an efficient blade, but is shorter than a claymore. Also, a one-handed blade allows the wielder to carry a shield. In terms of firearms, a pistol weighs less than a machine-gun but isn’t as effective.
As many of you know, I’m an avid gamer. One of my all-time favorite games is Square-Enix’s 1999 Final Fantasy VIII, made for the PlayStation. It was challenging and fun to play, with entertaining side quests. I loved the music and the deep storyline. The characters were compelling and believable.
The one element that seemed illogical was Squall’s weapon, the Gunblade. Nevertheless, other fans loved it. However, while logic isn’t a thing when it comes to anime RPG weapons (witness Cloud’s Buster Sword in Final Fantasy VII), it must be considered if we want believability in our written work.
When it comes to weapons, it’s important that you research what might be most useful to your characters. Consider their strength and skills. Don’t introduce an illogical element, no matter how much you like it.
Writers of fantasy and historical fiction should do some fact checking:
Nerds on Earth’s Clave Jones says: So what would have kept a woman from wielding a longsword throughout history? Honestly, the only thing that kept more women from using swords is that they rarely got the training. It wasn’t the weight, certainly. And it wasn’t the awkwardness of the swing as swords were designed to be well-balanced and agile. 
Sci-fi writers, I suggest that for advanced weaponry, you should do the research into proposed future applications of lasers, sonic, and other theoretically possible weapons. Sci-fi readers know their science, so if you don’t consider the realities of physics, your work won’t appeal to the people who read in that genre.
For soldiers of any technology level, from Roman to medieval, to contemporary, to futuristic—armor will always consist of the same components: breast and backplate, shin guards, vambraces, a helmet of some sort, and maybe a shield.
These elements won’t differ much in their use. However, the materials they’re made of will vary widely from technology to technology.
For the sake of expediency and logic, garments that go under the armor must be close-fitting.
Expediency affects logic, which affects need.
The same is true for any occupation your protagonist might have–bookkeeper, lawyer, home-maker–the visual surroundings changes from genre to genre, but the fundamental requirements for each occupation remain the same.
In every aspect of a world, expediency decides what must be mentioned and how important it is.
Beneath the obvious tropes of a particular literary genre is a human being. No matter what genre you are writing or the level of technology, their actions and reactions will be recognizable and relatable to the reader.
We’ve mentioned the soldier, so let’s look more closely at their requirements.
For instance, in a battle situation, food must be extremely compact, lightweight, and must provide nutrients the soldier needs.
Nutrition bars, jerky, whatever you choose, soldiers must eat, and battles don’t pause for dinner. Think about the battle rations, how much the soldier carries, and how she carries them. Weight and the amount of space rations take up are what limits the soldier’s supply on hand.
How do you fit a soldier’s battle rations into world-building? Casually, with one sentence, a few words. She unwrapped a ration bar and ate, ignoring the sawdust-like texture.
What basic things do you need in the real-world? You need food, water, clothing, and shelter, and a means of providing those things.
Characters need these things too, but they only come into existence at the time they are in use. Place the character in a room and call it a kitchen, and the reader will immediately imagine a kitchen. Mention the coffeemaker, and the reader’s mind will furnish the cups.
Need manifests in other, more subtle ways.
Do you require a way to communicate with others quickly? Messengers, letters, telephones, social media, or telepathy? Choose a method for long-distance communication that fits your technology and stick to it.
In world-building, how you fulfill the character’s needs shows the level of technology, the society they inhabit, and their standing within that culture.
This layer is easy to construct in many ways, but if you aren’t careful, it can be a stumbling block to the logic of your plot.
Credits and Attributions:
 The History Of Medieval Swords (And The Women Who Wielded Them) by Clave Jones, © 2016 Clave Jones for Nerds on Earth (https://nerdsonearth.com/2016/02/women-and-swords/ accessed 08 July 2020).
Excalibur, Eduardo Otubo / CC BY (https://creativecommons.org/licenses/by/2.0), Wikimedia Commons contributors, “File:London Film Museum (5094934492).jpg,” Wikimedia Commons, the free media repository, https://commons.wikimedia.org/w/index.php?title=File:London_Film_Museum_(5094934492).jpg&oldid=273444520 (accessed July 7, 2020).
Squall Leonhart, Final Fantasy VIII, Square Enix ©1999 Fair Use
Cloud Strife, Final Fantasy VII, Square Enix © 1997 Fair Use