Princess in an Iron Helmet (2006)

Original title: 転がれ!たま子

Tamako is 20 years old, lives at home with her mother (Kishimoto Kayoko) and teenaged brother, and simply refuses to grow up. Ever since her father left the family, she's stopped trusting people, and now lounges around in her own small, claustrophobic world. Wearing an iron helmet whenever she steps outside, she ventures only to her mom's beauty salon, the mechanic shop, and the bakery - the source of her greatest joy in life, sweet buns. Her world is static, insular, and safe, and there's no need to change - that is until her cat runs away, the bakery closes, and her mom falls in love with another man.