D is for determined
It was with a determined look on his face that Naru purposely let down his mental guards and opened the flood gates to the enormous power inside of him. He was determined to save his friends. Quite possibly the first he'd had beyond Gene and Lin;who was at first being paid so he wasn't sure they'd have been friends otherwise.
These people, his rag tag group of SPR are different to him. He cares what happens to them. Most of all he cares what happens to Mai. Young Mai who had wormed her way in.
He was determined to find his brother. He was determined to give him peace. He was determined to tell her the truth as soon as he could, and he was determined make her his.
He never failed when he set his mind to something. He had been determined to take his tests early and determined to get into college at a young age. He had been determined to get his doctorate(even if was just honorary right now) and he now going to sink every bit of determination into the tasks at hand.
He had never been deterred once he put his mind to something, and failure was not an option he would entertain.
These were the most important things he had ever done. For the most important people who'd ever come into his life.
He was determined not to let them down.