Haruka is not a Full fledged Demon. He is actually Demon x Vampire. Being born halfway like that, he's been treated badly by his comrades since he was born. Also grown in a strict family since he is an only child. When he was 12 (human age), He already gained everything he wants using his gifted powers that even surpass their elders in their family three. With his great powers and dark pass being treated badly, he gained a corrupted personality that always look down on others. He even granted to be the next Head of the family demon due to his great rare gifted powers but when he hits age 16 he abandon his family and go to the other world to start an adventure life and peace from the demon's family. But due to all this, How can he fall in love with Harue? That'll remain mystery~

Since he'd too powerfull he did not found anyone nor other species that capable to fight with him. So he never fight with anyone using his power 100% since someone can already die if he only use 20%. Normal human die with 5% power.
Merciless, Cruel, Sadist, Twisted
He always look at human as low life same as other species.

Psychosocial
Let Me Hear
Metal
Unravel