Lisa is a young lightly tanned-skinned woman of average height. She has black eyes and dark brown/black hair styled into a bob cut, similar to Sosuke's. For most of the film she wears a dark blue shirt and white pants, with a pink apron around the house.
Lisa is a loving, self-sufficient, and strong-willed woman. She is extremely headstrong and courageous, almost dangerously when it comes to her driving, but she always makes it out alright in the nick of time. She seems to be a local legend for this. Responsible and wise, she tries to raise Sosuke as best as she can, teaching him many seafaring skills such as morse code with signal lamps. She is still young and energetic, missing her husband and getting angry when he doesn't keep his promises to come home, but she doesn't hold grudges. A hero as well, she is compelled to go help the seniors even if it means leaving her children temporarily, and accepts Ponyo as her own without question. She is an outstanding mother and a great woman.
Lisa works at a Retirement Home in a small seafaring village, right next door to her son Sosuke's kindergarten. She takes care of the elderly for a living while her husband Koichi works as the captain of a ship. One day her son finds a goldfish stuck in a bottle and she allows him to take care of it without much thought. Careening around the mountain roads, we find out that Lisa is a crazy driver, racing a docking ship to get to work on time. Shortly after she drops Sosuke off, he gets in trouble and Lisa saves him from the water after Ponyo is taken from him by her father and his water spirits.
When they get home later that day, she encourages a sad Sosuke to leave his green pail as a signal for Ponyo to come home. Her husband ends up needing to take another shipping run and can not come home as promised, which makes Lisa angry. She tells him to bug off in morse code with their home signal lamp. Sosuke encourages her this time and she bounces back into a happy mood.
The next day, Ponyo returns in the form of a girl after opening the well of power and causing the ocean and weather to turn dangerous, tsunami sized waves and power outages forcing Lisa and Sosuke to go home early. Lisa appears to not know the concept of fear as she races the ocean itself to get back to their home on the high hillside just out of its reach. When Ponyo appears, Lisa accepts her just as she did when she was a fish, without a thought (even when she says her dad was an evil wizard and she swam away from home), and treats her as her own daughter. She feeds Sosuke and Ponyo honeyed tea and ramen, turning the scary storm into a fun game, distracting them with simple tasks like turning on the generator and setting up the radio antenna to contact the ships out at sea.
When Ponyo falls asleep and the sea calms down, Lisa leaves Sosuke in charge of the house and taking care of Ponyo to go and help the seniors that might be stranded.
Towards the end of the movie we find Lisa again, in conference with the Goddess of the Sea, Granmamare. According to the seniors, they had been talking all night and day. Granmamare appears to have explained to Lisa the weight of her responsibility if her son succeeds in saving Ponyo and swearing to love her forever. She would be Lisa's daughter now, and future daughter-in-law after Ponyo became human, after all.
After the balance of nature is restored, Lisa promises Granmamare to take care of Ponyo, and Lisa's husband returns from the ocean with all the other ships.