Mat Davis

Mat Davis is a protagonist of the Beyond the Blue series. He is the youngest son of Michael Davis and brother to Jason. Mat is 16 years old, and appears to be ruthless and acting on instinct, contrary to his brother who appears to be more focused and calm thinking. When they left the city and abandoned all search for his mother Mary, Mat tried to leave on his own and find his mother, but his brother and father stopped him and made him go with them. During the whole way to James' farm, Mat was angry at them and wouldn't speak much. 
When the group finds a dosage of the cure to the leeching, Mat steals it and goes back into town to find his mother. The others go after him, only to find him in his house, leeched as well. It appears his mother was already in the house when he arrived and attacked him. Due to him being unable to shoot her, she managed to bite him, and leeches grew inside him as well. Before this happened though, Mat was able to tie himself and his mother and the group found tthem both. After taking them back, there was some controversy as to who should get the dosage, but in the end Jason and Michael decided that it was best if they split the dosage and dosed both. There was a risk in case it wasn't enough for any of them, in which case they would lose both, but in the end Mat managed to recover after a painful procedure. His body changed a lot though,as after the de-leeching he noticed his abilities were over the top.
Mary on the other hand didn't make it through the de-leeching process, and the scientists attributed it wither to her age, the time she was leeched, or the low dosage, although the latter seemed unlikely, since Mat survived.
After that, Mat was devastated at the loss of his mother, but he was somewhat relieved knowing that he did the best he could. The rest of the group also forgave him for stealing the cure
Mat was distant and depressed for a long time after his mother's death, and wouldn't willingly help the group. MIchael eventually talked to him though and he came to his senses. 
When Christine is revealed to have cancer, he thinks of leeching her and then using the cure as a means to cure the cancer. 
In the last battle of the series (when everyone dies), Mat will be dying even before this and in the battle he will be the only one to survive. He will make it back where the doctors will say that the leeching abilities have a high cost at his health and he will soon die. His grandfather will then console him, and Mat will say that he preferred to have these abilities over time. He says that now he prefers time, as powerful or not, he would get to spend more time with his loved ones. The only thing he doesn't regret is keeping the powers to kill more aliens. James then consoles him and cries, as Mat leaves his last breath in the arms of the his last biological relative