In the classic Madhouse Studios style (with Yutaka Minowa character designs) from the 1993 film Ninja Scroll.

ILLUSTRIOUS: Strength: 0.4 - 1.2
SD1.5:
Weight around 0.5-0.7/8 --lower the weight even more if it's too much--
0.3 perhaps for merging these characters with other characters.

For some preview images I used higher CFG with the Dynamic Threshold Extension
Prompts (applies to Illustrious except for the activation tag)
Ninjascroll
Traditional Media
retro artstyle
90's anime style
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Characters:
Not trained on names.
Add brown/black/yellow eyes and eyelashes in the prompt for more accuracy.
Jūbei - (1boy, solo, male focus, dark skin, brown eyes, eyelashes, hair over eyes, lips (neg-red lips), manly, brown hair, ponytail, Japanese clothes, holding weapon, holding sword, katana, hat, ajirogasa, samurai), fighting stance, battle, open mouth, teeth, clenched teeth (Include: 'perfect teeth' - if need be)
Kagerō - (1girl, black hair, short hair, eyelashes, brown eyes (or) black eyes, red lips (or) lipstick, purple headband, forehead jewel, ninja, gloves, fingerless gloves, short kimono, knife, pale skin)
Tessai - Stone Man - (rock, rock skin, stone skin, manly, muscles) <-- male focus may turn him into Jubei.
Benisato -Snake Woman - (black hair, long hair, eyelashes, yellow eyes, red lips (or) lipstick, smile, kimono, fingernails, nude, bare shoulders, snake, pale skin) -- Extra: Dragon (helps produce the snake sometimes), tentacles (mostly cursed though).
Genma - (black hair, short hair, hair over eyes, eyelashes, black eyes, manly, muscular, pectorals, thick arms (possibly), chin, sideburns (not in the prompts but he has them), serious., smile, smirk, dark skin.
Possibly more accuracy for him with prompt -> Red theme.
Other characters may appear but less so.
Might also be able to get --
Dakuan - (old, old man, straw hat, ajirogasa, hakama, haori)
Mujūrō Utsutsu - Blind Samurai - (eyelashes, closed eyes, black hair, long hair, haori, hakama, hakama skirt, holding sword, katana, bamboo forest)

LANDSCAPES:
no humans, scenery, indoors, outdoors, grass, valley, snow, desert, moon, building, architecture, east asian architecture, water (also include: Inverted reflection), sky, cloud, bloom (can help for the overall style), fireflies, field, flowers, tree, waterfall, plant, star (sky), wooden floor, mountain, fantasy setting, landscape, etc.

MONSTERS:
Monster/Tentacles/Snake/Scales - (2m Karras works pretty well for them) and can make some pretty cursed looking stuff since it's not really trained on any monsters; Just the snakes crawling on Jubei/snake woman, etc.

Blood can be generated

• Blue, Red or Green theme (for a possible base but not necessary though) - Trained more on blue.
  Blue - Night, Night Sky, Dark -- And for a better chance at lightning effect: electricity, bloom, monochrome (or 'spot color')
  Green - Bamboo Forest, Kagero, Jubei, hetero, (or -- 'couple, embrace, hug')
  Red - Building, Burning, (Fire, Flames, Blaze -- Not in the prompts though) and Jubei/Genma may show up.

Negative:
White border
Black border
Pillarboxed
Anime coloring
Monochrome
Topless (Female characters like to generate nude sometimes)
Painting/oil painting (if it's too 'messy')
Muscular,/thick/buff (if the males are too beefy)
Scar
Headband
Forehead jewel
Nude
Blood
3D
Realistic
1other
hetero
2girls
2boy/3boys/6boys/Multiple boys
Malformed sword
Nipples
Blood on face
2000s style