The Elementals

There are humans... and then there are monsters.
Monsters have lived among the humans long before anyone could remember. There are many different species and many different alliances, but they all live in harmony, lest the humans find out. However, the tensions between races don't allow co-mingling. Even if two different species fell in love, monster breeding is different from human reproduction. There is never a monster that is a member of two races. Until now.
Before each monster is sent out into the world to fend for themselves, they are required to go to a certain school to learn about humans and how to control their powers- the School for Monsters. At the School, each monster will obtain a Spirit that will guide them along their paths, assist them with their powers, and, on very rare occasions, conduct a Spirit-Binding, a sacred ceremony that binds the souls and Spirits of the two participants together- in human lore, they are known as 'soul mates'.
After the Great Devil War, the 8 Great Heroes that fought the evil Devil King have disappeared, leaving one thing behind- their children.
Love is a burning fire that consumes all obstructions, but some obstructions are necessary to hide the truth. The world changes around four mixed race children as old evil rises again and dead Heroes return- in unexpected forms. Can the quartet finish what their Great parents started, or is tradition too strict of a rule on society to help them?