Mikaela is kind and upbeat in spite of the harsh events in his childhood, when he was abused by his parents and then dropped out of a car. He was then taken in by the Hyakuya orphanage. He was able to keep smiling and be happy because of his adopted family at the orphanage and even managed to befriend the extremely stubborn Yu. Mikaela was shown to be cunning. He allowed Ferid Bathory to drink his blood in exchange for good food, but Mikaela's true purpose was to steal a map in order to escape with the other children.
(Source: Owari no Seraph Wikia)