Aosa

is a medical-nin of the Land of Calm Seas and Mozuku's sensei.

Background
When the daimyō restricted the medical treatment during an epidemic, seeking to financially profit off it, Aosa secretly developed a cheaper and more effective treatment for the population. However, the daimyō discovered this and sent his elite assassins to eliminate him and his fellow students. Before being forced into hiding, Aosa gave enough money to his student for them to make the journey to his close acquaintances abroad.

Personality
Aosa is a kind man who cares about the safety of his village. Aware of his daimyō's callous nature, he was willing to risk his life for the sake of others. He greatly loved his students. His compassion and efforts earned him great praise and loyalty from his students.

Appearance
Aosa is fair-skinned man of above-average height. He has sharp, blue eyes, and short, brown hair combed to the side. He wears blue robes and round, frameless glasses.

Abilities
While little is known about his abilities as a shinobi, Aosa is revealed to be a brilliant researcher, having developed on his own means to cure an entire epidemic. He is also apparently a capable teacher, having taught his students how to use medical ninjutsu and continue his work in his absence.

Path to Becoming a Ninja Arc
As Aosa waited at a checkpoint for his students, he instead was met by Kawaki, who regretfully told him of Mozuku's sacrifice. Truly saddened to hear of his demise, Aosa proudly took the medicine Mozuku refined along with the remaining money he got from him, promising to heal his nation in Mozuku's memories. Kawaki also told him of Mozuku's location so he could retrieve the boy's corpse for a proper burial.

Trivia

 * means "sea lettuce", a type of edible green algae.