Character Creation Guide

Process

Creating a character is a multifaceted process of using the mechanics of the game to bring to life your concept of the character you want to create. I would encourage you to read through all of this and explore the various options before you commit to any particular idea you have. I will go through the creation process from the most to the least important.
The main aspect of your character is their Class, which is the fighting style of your character. This will typically be either a magic or physical based class. Note I have two custom classes created: the Shrine Maiden Class, Soldier Class, and Mystic Class. After you have found a class that fits what you want, you can choose a subclass. I have a list of Custom Classes and Subclasses on top of the basic ones here. Sometimes its better to actually base your class choice on the subclass concept, since the subclass is going to be much more specific to what you actually want, like how playing a geisha subclass specifically might be more important to you than playing a bard of any kind.
Then Special Races, for which this campaign uses its own special list considering the cultural influence of the setting. While this isn't an exhaustive list of potential races, it represents the primary ones most likely to be chosen for the setting
Now choose your character's background, which will inform the skill sets and story of your character's past
After this is your character's non-mechanical traits. This includes their personality traits, goals and ideals, backstory, their flaws, and lastly their friends, family, enemies, and other people they know. Adding things like political affiliations, and group or faction memberships will give a lot of fuel to your character's involvement in world
Add a description or depiction of your character's appearance, and other flourishes like where they are from. How is their race, class, culture, and background as well as personality feeding into their appearance?
If your character derives magic from a god or other supernatural force, consider grabbing something from the list of Shinto gods listed here: Kami. The gods have real significance and connection to certain things, places, and people, so it might be better to choose something that thematically makes sense for your character
Choose their weapons or spells. Ideally this would be inspired by the culture and themes of your character. The standard list of D&D weapons could easily be re-flavored to represent a Japanese style. A list of modern Weapons is available too for relevant classes. As for spells, sticking with a common theme like "lighting spells" or "charms spells" while sprinkling in some other types to round it out can give your character an iconic theme without leaving them as a one trick pony.
A special mechanic I've created for this world is "omamori" which are charms the characters can wear that give them small passive buffs. Pick one: Omamori.
Over time you will also be granted various upgrades to your character, allowing them to be more iconic and special. To empower the DM to give you the kind of upgrades you want, come up with mechanics or thematic you wish to enhance or obtain. These could be upgrades from other classes and subclasses, or anything else. Imagine what you want your character to be like and be able to do when they are super powerful and legendary in status.
Most importantly though, if the concept for your character doesn't work mechanically well but you love it, let the DM know and they can tweak and fudge some stuff to allow you to have the character you want. Being able to have fun creating and playing the character you want to make is more important than whether the rules says they should have higher intelligence or dexterity, or whatever the conflict may be.

Creation Tips

Having spent a fair amount of time running this campaign, I have several observations regarding what makes a great character to play.
Your character must have a good, fun, and durable reason to be a member of the Kenpeitai. If your character doesn't really believe they should be where they are, and doing the things they're doing, you will consequently not be invested either.
Your character should be able to get along with all of the other player characters. This means loner edgelords, and needlessly aggressive and divisive characters that sound fun on paper, will end up grinding group cohesion, and therefore fun, to a halt. This isn't to say you cant have differences of opinion, just that those shouldn't be so strong that they lead to constant infighting
Creating connections to a lot of interesting people and groups will give you endless opportunities to do fun things and develop your character and their relationships throughout the campaign
Your character should try to fill a unique role, and should avoid stepping on the toes of the other characters. A charming trickster character doesn't need another charming trickster character to try to fight over scraps of opportunities. Have your character be good at a narrow set of things and it will be more fun to rely on your party for the rest.
Avoid making characters that are either too serious and realistic, or too silly or over the top. An overly serious and grounded character can lack opportunities for humor or the kind of supernatural antics or things that are more exciting than real life. Conversely a character that is a walking meme will be incapable of producing drama, stakes, or an investing character arc and story. Communicate with your DM how you want your character arc to develop and conclude (assuming you have opinions on how you wish for it to happen, its okay to give the DM that control if you would rather leave that open ended). How do you want certain character relationships to develop, and what kind of upgrades and thematics do you want for your character. The DM is your ally, and the more your give them information and guidance, the more the DM can help your tell the story you want. Try to make your character fit within the world and its logic. Your character shouldn't be an entity above and apart from the world, looking at it as a playground it is uninvested in. Rather your character should have many things and people they care about, and a sense of belonging within the world. There should be a reason and purpose for every aspect of your character rooted within the context of the world they were born into