Her father was a fire demon so she got this hot body constitution from heredity, so i though it would be a lot more open, and this heredity thing also the same reason she has the royal/monarch fire magic, plus her mother was also a legendary mage thought not as strong as the vampire sage.
And for some people asking if Makoto will build a harem, yeah he will build it in the future, tho it will be pressed by the women side.
Spoiler in a spoiler, his harem in translated WN was already included Lucy, his "lamia" childhood friend(that thought to be dead in 1st chapter), and Sophia the water priestess, there is still no progress with Noa/Noah, but Noah and Eiru/Eir the water goddess helped him a lot too