When his little sister was mauled by a rabid dog, James had to make a tough choice. She was only 6, and slipping, and the only chance of saving her was a blood transfusion, and a new kidney. He offered almost immediately to give her his own blood and kidney, but she required a large amount of his blood, and even then, there was a chance she wouldn't make it anyway. He took the risk, and had his kidney removed, and gave her all the blood he could, though it left him incredibly weak... he was risking sickness himself.
She lay near death for a whole week, and he stayed with her that whole time, needing a walker just to get around. The doctors told him she would either pull through soon, or they would lose her. He took her limp, almost lifeless hands and made a promise to her. If she lived, he would make sure he would always be in her life and make her happy.
She awoke, and began a slow recovery. He kept his promise, and now she is a young woman of 17, him being 21. He has his own place, and having no where else to go for now, she moves into his spare room. She suffers a very bad break up, and James remembers his promise to her. He'll do anything for her... even if it means loving her.
I could play either of the two :)
The guy... lets just say he should be perfect big brother material. The girl... I have a better idea of how she should be. Typical silly girl into cuddly stuffed animals, cute, loving and giggly.