Her culinary style is just as unique.
She sculpts rice colored with egg yolks into the shape of a dinosaur and fashions its eye with sliced cheese and strips of seaweed. Star-shape pieces of okra adorn the belly.
"I just wanted my son to have fun when he goes to day care on Saturdays," explains Ms. Shimomura as she uses tweezers to place tiny teeth-shape bits of cheese in the dinosaur's mouth.
Spending hours meticulously perfecting a meal that will be gobbled down in a school cafeteria by her 6-year-old son hardly seems like time well-invested.
But lunch-box art marries the age-old Japanese penchant for precision and aesthetics with the country's modern, shrinking, affluent nuclear family, where fewer children mean moms have more time and money to lavish on their little emperors. The intricate presentations are also a public way for mothers - who often forgo careers to cater to their families - to demonstrate their devotion to motherhood, dedication to their children's nutrition and creative skills.
"This is rather about my pride," acknowledged Miho Tsukamoto, 41, the mother of two in the western city of Osaka. "My son boasts about my cooking to his friends, so I can't stop doing this."
The boxed lunch - known in Japan as bento - has been around for a long time. The prototype of modern bento dates back to the late feudal period between the 17th and 19th centuries. With industrialization came mass production: office workers buy them in train stations, convenience stores and food courts.
Nursery schools typically require children to bring home-cooked bentos and some wives make them for husbands. The creations of Ms. Shimomura and others, however, go way beyond the humble arrangement of fish, rice and vegetables that Japanese subsisted on in the past.
The lunches - like other types of Japanese art - often feature a seasonal motif such as fireworks in summer or snowmen in winter. Others recreate popular cartoon characters or famous people such as the Japanese pop duo Puffy, or even Mozart.
Details are prized. Slivers of carrots are sculpted into a crab on a bed of rice; avocado slices, fried tofu and black sesame seeds morph into Frankenstein's face.
"I never make the same thing twice. I just think about what to make next time," said Ms. Shimomura, 38, as she leafed through albums of digital photos of her work at her home outside Tokyo.
Housewives have taken their lunchbox exhibitions online, where Internet journals feature up-to-date photos of the latest works. Cooking books catering to the trend are proliferating, and companies even hold contests.
The blogs provide a forum for mothers to exchange esoteric tips such as how to dye egg white blue.
The trend has struck a chord with stay-at-home mothers, many of whom retire early when they have children, but still have plenty of creative energy to spare.
"Beside wanting to create things, you also have other motivations, like you want to please someone, or be famous for what you make," said Kunihiro Nakazato, the editor for Tokyo-based publishing company X-Knowledge Co., which has put out at least one bento cookbook.
Mari Miyazawa, the host of e-obento.com, said she started making bento to save money, but now it's become a full-time job: she's written three cookbooks and is one of the most recognized lunchbox artists in the country.
Ms. Miyazawa, 45, a former computer graphics artist, says that making bento art is more demanding because it's impossible to edit - you either get it right nor not.
"I finally found the perfect medium," she said.
MADE WITH CARE
The boxed lunch, also known in Japan as a bento, consists of a portion of rice, fish or meat and a variety of vegetables. These small containers are where many housewives create their artwork. Meals can be very elaborate and often arranged to depict a picture or object.
The intricate presentations are a public way for mothers, who often forego careers to cater to their families, to demonstrate their devotion to motherhood, dedication to their children's nutrition and creative skills.