Matsu is the initial persona of Maki Sonomura in Megami Ibunroku Persona. She is called Maria in Revelations: Persona. In the recently re-released version of Shin Megami Tensei: Persona, her name has been changed to Maso.
Matsu is a Chinese goddess that protects fisherman and sailors from dangers of the sea. As a mortal, Matsu learned how to swim at the age of 15 and quickly became one of the best swimmers in her village, eventually becoming a guide to sailors and fishermen by wearing red garments on the shore to attract their attention back to the village. On the night of a storm, Matsu's brother and father were out at sea fishing. Their boat broke and they started to drown. Realizing that they were in danger, Matsu fell into a trance and tried to guide them back home. As she was doing so, her mother found her and awakened her from her trance. Though she was successful in helping her father home, her brother drowned.
Shin Megami Tensei: Persona