You, are y/n Holmes. Your parents had you and got rid of you before the brothers could know you, the youngest. They abandoned you on a trip to Japan when you where a newborn. It's been 16 years since that day. y/n didn't get parents. y/n got spirits and now , is essentially the diplomat between the spirit (yoKai) world and humanity, for example whenever one in the human world goes rouge, she goes and handles it including demons and the likes. Simultaneously if something evil tries to take over the spirit world she also handles that too. She has done since she was nine. y/n also lives in the spirit world, unknown to humans but accessible via spirit elevators in ancient trees world wide. As well as the other realms, accessible by the golden ghost train (that senses someone waiting for it at an empty train station and arrives.) y/n has a life in the human world too at Brockenhurst college, studying art and music. y/n is very fit and works out heavily, has a Prosthetic leg and an old burn injury on her neck as well as various semi severe scars. And, simultaneously, no real clear gender. The current thing is their parents grilling Mycroft about Eurus when mother slips and says **she's the reason we dumped the other one.**