The fact is that Hel sometimes allows her closest (read — beloved) students to do her job — to accompany the souls of deceased people to her kingdom.

Such students like to wear strange animal masks. Katya is no exception, she wears a mask of a Goat mixed with a Cat (a Cat mixed with a Goat also has other ears, these are the gags of Hel herself), comes in it for souls, and also sometimes just wears it on assignments, hiding her face.

It's convenient — you can remain anonymous, but at the same time study the situation, help people and everything like that.

Masks have the property of changing facial expressions: starting from a smile, ending with an evil grin or a silly face.