The First Crime
Big Mama is a servant of the Kizaki household.
Big Mama is an elderly woman. She wears a maid outfit, with a deep color of lipstick. She has Crow's Feet and a mole on her face.
She is very strict and greatly inforces the rules of the house, such as stopping Rio's training when her father was away and taking away hero accessories that she buys, though she did allow her to keep a belt her friend gave her.
She is also very protective of the mansion, stating not even a mouse will get past her.
At some point Big Mama bacame a maid for the Kizaki family.
First Crime Arc
Big Mama first appears to interrupt Rio's training with Billy. She voices the fact that her father wished for her to stop this as well as preventing her from getting away with it when he is not home. After a quick banter with Billy, she drags Rio out of the training room.
Big Mama later appears after Ratman broke in, stating that she would not even let a mouse get past her. After a short fight, Ratman makes his escape outside a nearby window.
Hero Awards Arc
Days later after the hero awards, Big Mama catches Rio playing with a hero belt. She then talks with Rio about the belt and decides to let Rio keep it, after she finds out that it was a gift from a friend.
Sometimes later, Big Mama is at the airport with Rio and Shouichirou says good-bye to Billy.
She is shown to be quite strong, fending off Ratman when he broke into the mansion. She seems to use a Fencing Style with her mop.
Nothing is known about what kind of relationship that Big Mama has with Rio, but it is shown that she doesn't like it that Billy is training Rio and that Rio is buying super hero stuff.
She appears to dislike him as he encourages Rio's training, wishing he would go back to the military. However they are able to fight well together.