It seems that the author chose the (non-Japanese) name "Vierca" (maybe related to the Slovakian name Vierka?), with the katakana title being the closest-approximation. It doesn't seem they meant to romanize "Viruka" (which doesn't appear to be a name in any language).
Imagine if something was published in Japan with the title "アイ アム ジョンスミス" with cover art including the English phrase "I Am John Smith".
While it would be totally fair to say that it's more faithful to title it on Mangadex or elsewhere as "Ai Amu Jon Sumisu" to reflect the katakana title, it wouldn't be correct to say the author attempted and failed to romanize their title by not writing it that way elsewhere in their book.