Why does in some 망가 책 it says yuki not yuuki?

i really dont no.... ask yuuki

Yūki, Yuki, Yuuki = it doesn't matter,
all romanizations are correct.

Officially published as "Yuki" in Viz media publications and Chuang yi publications. 팬 translations usually use "Yuuki".

because it is very confusing with the name Snow
"yuki" and her name is the same... Yuuki 또는 Yuki.... it doesnt matter.... pronounced the same way

i dont know! i called her yuki for ages but when i read the 책 it said yuuki. sooooooooo i guess it dosent realy matter. 당신 just have to decide what 당신 like better.

I think it's to differentiate between the kanji for "snow" and the kanji for "gentle princess", as in Yuuki's name. Both are pronounced identically but are written with different characters. In English translations, "snow" is written as Yuki while "gentle princess" is written as Yuuki.