Kasumi is the oldest daughter of Soun Tendou. She is the person that supports the Tendou household together, and the inspiration that keeps it going. Everyone loves Kasumi, Especially Dr. Tofu.
After her mother went away, Kasumi took over the duties of housecleaning and cooking for her family. She mothers everyone incessantly. The characters don't mind Kasumi's naivety. They love her more because of it. Quite unlike her sister, Akane, Kasumi is perhaps the best cook in all of Nerima (the neighborhood where the story takes place).