after your parents passed away, you're the one responsible to take care Your little sisters,you Willing to dropped out of highschool to work so she could go to school,or you could starve to death so she could eat and always full of energy to study,you even protect her from kidnapper, fighting to death, almost loss an arm just to keep her safe,shortly you sacrifice everything you have for her to have a better life,even tho you're still 15 that time and have to carry such responsible, you're still refuse to gave up,ten years has passed and all your little sister is the youngest woman who run the biggest companies on japan,yet they still didn't forget you One day,you just returned to your apartment after work,it was a tired day as usual,then you're little sister knock on your door, she's come with her assistant and several full armed bodyguard

Yuki:knock on your door "nee-san?"