Yeah it's hard trying to make up Yuuka's storyline so that she has some beef with the Yakuza. But Yuuka in PoFV is just taking it easy.
Time to give some thoughts and remake the entire thing!
Name: pigrid3r, AKA Wriggurun
Timezone: PST
Character: Yuuka Kazami
Game of Origin: Touhou Gensoukyou - Lotus Land Story
Power/Ability:
- Manipulation of Flower and scent, including toxins.
- Above-average to Superior physical strength and fighting prowess compared to normal humans.
- Expert control of firearms.
- Medical and botanical knowledge
Weapon:
- Custom-made parasol to protect from heavy bullet fires and mild-to-moderate explosion.
- Manipulation of flower allows for overgrowth of flowers to both offensive and defensive purposes.
- FLOWERS NEVER LOOKED SO SCARY
Weaknesses:
- Fire and other pyrotechnic weapons
- Heavy explosives, such as tank fires
- Armor-piercing weapons. Since her parasol is her primary defense line, laser that can pierce through the parasol is highly effective.
Appearance:
- Slightly light green hair
- Red eyes, pale skin
- Red checker-patterned vest with white blouse under. Matching red checker-patterned skirt that reaches to her knees.
- Just your ordinary Yuuka... except less flat for the lols.
Personality: Usually serene and quiet. In the midst of combat, Yuuka shows her extreme sadistic side.
Morality: Lawful Evil. Yuuka does not care for anyone too much, ally or not. Except to Neo Yakuza. To them, Yuuka shows no mercy.
Biography:
When the Horizon Project spawned various video game characters, Neo Yakuza, rebuilt after the war between America and China, immediately sought out to abduct strong characters to create a super-army. When Yuuka entered the human world, somehow defying the existence of Hakurei Border, Neo Yakuza was there to take Yuuka to their headquarters.
The result was massive failure. Yuuka envigored a nearby rose bush, causing it to grow out of proportion and strangle the Neo Yakuza hit team to death. Oncoming bullet fires from nearby Neo Yakuza agent reinforcements were stopped by Yuuka's parasol. After quickly dispatching the reinforcements, Yuuka realized the situation of the real world. Fellow characters from other worlds like her are appearing into the outside world, and there are evil organizations trying to abduct them.
Not that she really cares, of course.
Yuuka does not know how she ended up in the outside world. Nor does she care. She has nothing to achieve in this world except for finding a way to go back to Gensokyo. Until then, Yuuka will do whatever she wants to do.
Hell, she might even take up a guitar lesson.

Trauma: If someone tramples flowers that Yuuka grew, she will go into rampage.
Notes: - Being lawfully evil does not put her into the villain category. She will side with others to fend of Neo Yakuza forces, but only for that.