I'd honestly just recommend my SDXL Pony version of Yuki. Still, since it was requested, here is a SD 1.5 version.

Trigger word:  Yuki Suou 

Keywords you’ll almost always want to use:

Yuki Suou, brown hair (black hair may work better in some cases, especially with scenes with darker lighting), long hair, purple eyes, collarbone, hair between eyes, 

Appearance keywords:

Half updo, Ponytail, bangs, school uniform, pajamas, red bow, white shirt,  Nijigasaki academy school uniform, yellow shirt, jacket, hood, pink hoodie, white shorts, jeans, blue jacket, pleated skirt, collared shirt, blazer, 

Other helpful keywords:

one eye closed, tongue, tongue out, downblouse, <:) , :D , :O,  cleavage, open clothes, smug, smirk, blush, hand up, V-Shaped eyebrows, manga (object), couch, book,