She went down with a smile.
Because Himeko knew that the anti-Honkai serum would work on Kiana. It had to. If not, her death will have no meaning.
Who knows what happened to Fu Hua. She doesn't know why she saw Fu Hua in her cell. Was she a hallucination or something? That's unlikely because she led Himeko to the Vermillion Knight battlesuit.
Before all this messy Herrscher of the Void reawakening stuff happened, Himeko wanted to snag a guy and get married or something before her shortened lifespan got her.
But it seems that in order to give one of her students a happy ending, she would have to die.
Whether it be from an even more shortened lifespan due to not taking the anti-Honkai serum for herself and extending her life or to the Herrscher killing her, she will turn Kiana back to normal.
And so she did. With a smile.
As her vision blackened, she wished. She wished she could've been able to do more. Marry a good guy. Teach her beloved students more. Live longer.
But as how life is, she will meet her father soon. Maybe in heaven or maybe in hell.