Hojoon is an Undine, a water elemental, he was born to pureblood Undine parents. Most Undine children are only half-breeds as male Undine are almost unheard of, they are very rare and don't usually live long as they are seen as "bad omens". Undine are majority women, they take the form of a human but with pale skin tinged blue, but are born without souls. They must marry a human to gain an immortal soul but this also shortens their own life span, thus most Undine children being only half Undine.
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The half Undine children look like regular humans but posses not only basic Undine powers but a human soul too. 

But he doesn't let it get him down, he's generally friendly and fairly optimistic, sometimes a little clumsy.