Yuko, 38, an office worker, has keitai straps appropriate for each season -- furry ones for winter and beaded ones for summer. When the temperature changes, she adds another to her collection.
"It must always be original," she says, holding up her recent favorite: a keitai strap her friend bought her from Tokyo Disneyland with Mickey Mouse-shaped beads on it. "It's a limited edition," she says proudly.
"When I leave my wallet at home, I can survive by borrowing money," she says. "But if I forget my keitai, I'm worried all day because there's no substitute."