Mathias Luna Tearmoon is the current Emperor of the Tearmoon Empire, and is the father of Mia Luna Tearmoon, his only daughter.

He is a harmless man, according to Mia, and an overly doting father. He often takes his expressions of his love for only his daughter a bit too far, much to her dismay and embarrassment, such as making her punishment for being reckless by having Mia call him dad instead of father for an the better part of a year. Due to his love for his daughter, Mathias doesn't care what the opinion the people of the Empire have of him, and only cares that Mia likes him.

While Mathias might seem to be rather poor as an Emperor, he does well at ruling the Empire as best as he can, though it is not enough to prevent a revolution from occur and his own execution. While opinions of him may be low the majority of the time, he has a majestic, commanding and imposing presence, fitting his position as the ruler of the Tearmoon Empire. Along with this, Mathias has been shown to know and be very careful about who comes and goes from the royal palace.

Mathias is shown to be loyal to his family, especially to his deceased wife, Adelaide Luna Tearmoon, since he has never once considered remarrying of even looking for someone to fill her position following her passing a few years after Mia was born. While she may have been the one his mother chosen for him to marry. Mathias has stated that Adelaide is the only woman he has ever loved, not including Mia, and that he fell in love with her at first sight. His love for her is very deep, and he has told Mia that if the two of them were drowning, he would choose Adelaide over Mia.