Lore
Setting: Set where Reimu (and other characters her age, like Marisa) is in her late teens (at youngest, she's 17, while at oldest, she's 19).
Synopsis: A few years after her latest adventure, Reimu has begun to make her own choices in life, becoming more independent as she strives to forge her own future. However, a new threat is arising from within Gensokyo; a threat that will determine the futures of EVERYONE within it.
Changes
The STORY change is a result of me not being a fan of ZUN's storytelling. I find certain stories in the Touhou games to be boring and not as serious or interesting as they could've been, as they have great potential.
Most CHARACTER changes are due to the characters' age and the AU's plot. This includes a more mature personality (while staying true to canon) and appearance (while not over-exaggerating). At most, the human characters are a full foot taller and have a lean, athletic, or muscular build now, due to the amount of fighting that's happened as a result of the incidents.
A few human characters has headed to the outside world for a different path in life. These include Sakuya, Marisa, and Reimu.
Out of all the characters, Reimu is the one who changes most significantly. She has grown taller, has shorter hair, has a more muscular build, and has become more serious.
As stated earlier, she has begun searching for her own path in life. A life OUTSIDE of Gensokyo and being a shrine maiden. This has caused some friction between her, other maidens, and of course, Yukari.
Characters
Major
Protagonists: Reimu, Marisa, Sakuya, Remilia, Sanae, Kanako.
Support: Sendai Hakurei No Miko, Yukari, Ran, Byakuren, Toyosatomimi no Miko, Alice, Oni Miko and White Reimu (treated as ancestors of Reimu), Dragon God.
Antagonists: Maga-Reimu (Wicked Reimu), Gensokyo, and certain residents.
Minor
Pretty much the rest of Touhou's cast of characters, including the rest of Japan.
About the Sendai Hakurei No Miko
Okay, so given that this character is the most popular OC in Touhou content, I would like to go over my interpretation of her. I have given this interpretation of her the name of Megami, which is Japanese for "goddess".
Firstly, she has four official forms. Her human form doesn't technically count, as it evolves into her base form.
Her human form was what her base form evolved from. It is very similar to her base, with the exceptions of being shorter, having shorter hair, a lean and thin physique, and black eyes. This is what she was like when she was in her early 20s. After dying, this is what she looks like in the afterlife, though still has access to her various forms.
Her base form (provided by Rion on pixiv) is her fueled with her powers as a shrine maiden. In terms of appearance, this is what she looked like when she was at her prime and raising the infant/toddler Reimu, so in her late 20s to early 30s. Her eyes are blue, she's lean and fit, and has short hair.
Her demon form (provided by warugaki on pixiv) is her borrowing the powers of Hell. Due to this, her appearance changes to having much longer hair, a more voluptuous body, an increase in height, and piercing red eyes, all matched with a cold-blooded killer-instinct demeanor.
Her angel form (provided by lockheart on pixiv) is her borrowing the aid of the heavens. Her appearance is similar to her demon form, with the sole changes being her yellow eyes and her overall demeanor being less threatening and far more calm, though still intimidating.
Her end form is an older version of her base form, as well as much weaker, due to her shrine maiden powers sweeping away as she gets older. Her accelerated aging is a horrendous side effect of her power usage and consumption, so while she in her late 30s, she looks like she's in her 50s to 60s. Her hair is now gray. Her eyes are white, due to her power usage. Her physique is frail and thin. However, she is able to use her base form's power and transform into a more youthful state, at the cost of her power becoming even weaker. This is ultimately what takes her life.
In regards to her personality, in both her base and end forms, she has a gentle and more cheerful demeanor surrounding her. She is filled with so much love in her heart that she can't bare the thought of losing someone she cares about. She can be a worrywart, but she knows to trust people. In spite of her forms, this never changes. She is best described as a Mama Bear/Wolf and is a good mother to Reimu, in spite of Sendai's struggles and challenges.
She likes SOME of Reimu's friends, namely Marisa, Sakuya, and Sanae, as she believes them to be good influences on her. Others, on the other hand, she finds intolerable and wishes she could knock some sense into them. She is NOT pleased with Yukari's tutorship of Reimu and views Kasen as a better mentor. She wishes she could tell Reimu the truth behind the Hakurei God and wishes she could urge her to be the Shrine Maiden of the Dragon God.
The former Miko has disillusions with Gensokyo and the Hakurei God, due to certain accidental discoveries that she hadn't expected. These disillusions extend towards Yukari, who she believes has known this from the get-go and refused to tell anyone.
In terms of fighting prowess, just watch this video on youtube: watch?v=I5trgSvUAGM