Yasuko Takasu

Yasuko is Ryuuji's thirty-three-year-old mother, though she refers to herself as eternally twenty-three; she has large, F-cup-sized breasts. Soon after Ryuuji was born, her husband died which left her to raise her son by herself. She works at a hostess bar named Bishamonten Kuni where she goes by the name "Mirano" and single-handedly supports her two-member family financially. However, she has a childish personality and since she works, she entrusts the household chores to Ryuuji. She instantly takes a liking to Taiga and already regards her as a member of her family.

Later in the show, Yasuko reveals that Ryuuji's father didn't die. He basically abandoned the two of them, leaving Yasuko to raise their son by herself.
(Source: Wikipedia)