Exactly who, should protect who? Does always older brothers should protect younger siblings? But then, who should protect older brothers when they're in danger?

A girl came to this world. She came alone. A girl named Aya. She have an older brother. A twin brother. So how dose she have a twin brother when she came alone, you ask. It's wery simple actualy. That is where i came in.

Who am i? Oh, I'm just another girl travelng in time.Nothing special about me. Just mabie my skill.