Frostingface

Breathing Style

Decide what Breathing Style you want your OC to utilize. Different bodies are suited to different Styles, so keep that in mind as well. Here is the list of canon Breathing Styles as well as what is the main quality that makes the user capable of using the style, how many forms the style has and what the style is known for;

Sun | 13 | The basis of all Breathing Forms, a lost art until Tanjiro rediscovers it. Immense bodily control, increased lung capacity, and stamina is necessary.

Moon | 16 | Known for erratic movements having a balance of offense and defense. Users must be swift and powerful.

Water | 11 | Known for the adaptability of the forms. The most common Style taught, as it focuses on the basics and fundamentals of sword techniques. Muscles must be relaxed during form use, users imagine creating and manipulating water.

Serpent | 5 | Known for using indirect and meandering attacks that are hard to predict. Users have good wrist flexibility, agility, and speed.

Flower | 7 | Known for repeated strikes and graceful cuts, similar to flower petals. Users of this Style have good lung capacity and go through intensive training to upkeep the immense physical ability required. Agility is tantamount.

Insect | 4 | Known for utilizing poison to bring down demons. Users must have strong and accurate jab as well as nimbleness.

Flame | 9 | Known for powerful singular strikes. Users focus on strength.

Love | 6 | Users have flexibility and brute strength. A sense of rhythm is also important.

Stone | 5 | Known for it's explosive strength. Users must be strong and firm. Repetitive action is a must.

Thunder | 7 | Known for being swift and zippy. Users must have incredible speed and leg strength.

Sound | 5 | Known for being flashy. Users must have a good sense of rhythm and good hearing, must be agile.

Wind | 9 | Known for using relentless consecutive blows. Users must be acrobatic and have increased endurance as well as a flexible torso.

Mist | 7 | Users are agile and swift. They relax their muscles and have precise footwork.

Beast | 11 | Known for being wild and jagged. Users have incredible touch-sensitivity, flexibility and combat instincts. Users must dual-wield. Stated that is unlikely anyone could master it other than Inosuke.

Custom Breathing Styles and Forms

When coming up with custom Breathing Styles, come up with a theme you’d like to have. What Breathing Style does it branch off of? What kind of movements and traits would that theme carry? What kind of weaponry would work best with those movements? Can you differentiate the theme from existing Breathing Styles enough? Sakura Breathing would be far too similar to Flower Breathing, Butterfly Breathing too similar to Insect, River too similar to Water, etc.

When coming up with forms for your Breathing Style, try to avoid repeats. More forms does not make the style more powerful, it just makes it convoluted.

Keep in mind that Breathing Styles are not magic, they do not have elemental powers. Mist Breathing does not literally produce mist, Muichiro just speeds up and slows down to disorient the enemy as if he was amidst a thick fog. Your character cannot literally melt into shadows or teleport. The effects we see in KNY are a form of visual story-telling and eye candy, nothing more. The elements we see are a way to portray to the audience the feelings of using and going against the techniques. Giving your Breathing Style abilities more akin to BDAs takes away their humanity and hardships. Your character is still human (unless you’re making a Slayer turned Demon, in which case, the BDA would very likely have to do with whatever Breathing Style they utilized).

If the Style you want to make is too similar to differentiate from an existing Style, you can always come up with a new form for an existing style. It’s fairly common for this to happen. We see it with Tomioka’s Dead Calm, we see it with the Rengoku Esoteric Art, and we see it during the Infinity Castle Arc too.

Here’s a list of the custom Breathing Styles we’ve made that are open for anyone to use:

Flight | Forest | Spirit | Archery

Katana and Other Weaponry

Each Slayer is equipped with at least one Nichirin weapon to take down Demons. The most common weapon is the noble (daitō) katana, of course. However, there are Slayers out there who utilize a different kind of weapon. Japan has many wonderful kinds of weaponry that could easily be translated into a Nichirin weapon. Even if a weapon is small and incapable of decapitating a demon, there is always the option of a poison user.

Here are some weapons of Japan:

If you want to go for archery, look at different kinds of bows and techniques from across the world. If you want specifically a Japanese archery style, look into Kyūdō and/or Kyūjutsu. Just keep in mind that compound bows were not invented until 1969, over 50 years after canon KNY.

Here is a list of the Nichirin colors associated with every Breathing Style. You can mess around with exact shades, as long as it is still in the realm of the color.

Sun - Black. The deeper the black, the more powerful.

Moon - Pale purple.

Water - Blue. Think something more akin to ocean blue than sky blue or cyan

Serpent - Lavender.

Flower - Light Pink. Think of the color of Sakura blooms.

Insect - Light Indigo. Somewhere between purple and blue, but light.

Flame - Red-orange. A saturated/bright and fiery color.

Love - Deep Pink.

Thunder - Electric Yellow.

Sound - Amber.

Stone - Grey.

Wind - Green. A light green closer to yellow than blue.

Mist - White with a blue undertone.

Beast - Blue-grey.

Blades also come with differing grain patterns as well, called Hamon.

Uniforms

Demon Slayer Uniforms can be customized to the wearer's liking, but the standard uniform is a button-up shirt with western-style pants or hakama accompanied by a white belt. A lot of Slayers will wear a haori as well.

Tops can be worn partially buttoned. Tops can have sleeves altered; some don't have any sleeves, some have short-sleeves, most have long sleeves, and some have flowy sleeves. The buttons on a Slayer's uniform will indicate whether or not your OC is a Hashira. Gold buttons are for Hashira while silver are for all other ranks. All tops have the kanji 滅 "Metsu" ("Destroy") embroidered on the back.

For pants options, some Slayers wear western-style pants (play around with different pants styles) or umanori-hakama, while most wear tattsuke-hakama. Some feminine Slayers may wear skirts of differing lengths.

Slayers may wear differing styles of Kyahan (the leg wraps seen on a lot of Slayers) as well as tabi and differing styles of shoes. Tabi can be paired with setta or zori. A Jikatabi is another good option for Slayer footwear.

Haori styles can be played with as well. They come in a wide range of colors and patterns, and it's possible to customize their shape as well. Some Slayers may wear them loose, some may wrap them around their torso like a yukata or kimono (remember, left over right), tucked into their belt. Some Slayers have shorter sleeves or shorter torso fabric than your average haori (like in Sanemi's case).

Background/Backstory

Decide what reason your Slayer has for being part of the Corps. A lot of Slayers have tragic backstories in which demons are involved, but not every Slayer has one. Some are there to test their skills. Some are there to protect people. Some are there to find something exciting to spend their time doing. Some are there to find a place to belong.

Anything else such as race, hair style and color, eye color, personality, etc can be up to your whims and fancies.