It's just a narrative trope to make the main character, Mizu, an "onryo" and an outcast. It's purposefully jarring that she considers herself "monstruous" but we, the spectators, see she is quite nice, actually.

Calling this "anti-white" (as the now flagged comment this) reveals more of the prejudice of the people claiming so.

> White people are monstrous and disgusting [...] it is completely OK to despise them and all prejudice against them is justified

Many Japanese characters in the show are equally monstruous, and the show's subtext is that it is not ok to discriminate Mizu due to her heritage.