Mika and the Hyakuya kids were more of lab rats. They get experimented every week. Yes,it was painful being experimented. All orphan kids gets experimented.
Yuichirou,the latest experiment. He was allowed to get out of his so called room which was more of a cell to him. He met the hyakuyas and was soon became a new member of the Hyakuya family.
One day,a mysterious fire started and destroyed the lab and also all the test subjects. Including the hyakuyas. The Hyakuya kids died in the fire,Mikaela got injured badly while yuu left without a scratch.
6 years,6 years of misery for Yuichirou. The humans build another lab and continued experimenting on other test subjects they can find. Then,one day,yuu got a personal caretaker since he can't be left alone all the time.
His caretaker was so familiar to yuu. But he couldn't tell why. And I'm assuming you all know who his caretaker is. Mikaela Hyakuya,age 18. Yuichirou's personal caretaker...