You could look for some plain cards with a Japanese print or photograph, or look is some of the Asian stores for little printed cards. A great substitute would be to use origami papers that come in those terrific designs that look like finely embroidered silk. Write out your invitation at the back of the paper and fold it up in a pretty origami figure.
You could choose to transform your party area into a Japanese garden, a tea house, or a Zen space. Choose a base of neutrals and accent it with bursts of bright colors like pink, red, aqua, or bright green. Keep it simple, remember the Japanese are masters of understatements. An easy centerpiece for the tables would be a single Japanese bonsai or an open fan highlighted with one or three camellia or gardenia blossoms. You could use paper cherry blossoms, if you can find them.
The food table should be decorated with a simple ikebana arrangement or even just a little tabletop waterfall. If you can find a Japanese doll, create a little vignette with a bonsai and a few paper umbrellas. Serve the food on stone slabs, wooden trays, or sushi “boats” if you can get them. Don't stick with just round plates; use a variety of shapes to add interest to the table.
You've got a lot of choices with the food. You could go all-out Japanese and arrange a ”make your own sushi” area. Set out all the ingredients for making sushi – nori squares, little balls of rice (keep your hands wet when forming these!), and a selection of fillings like cucumber sticks, mango or peach strips, kani (crab) sticks, omelet strips, sticks of yellow takuan (radish) pickles, and even strips of ham, if you want. You shouldn't prepare anything raw for this baby shower.
You could also serve ramen or udon noodles, a selection of tempura (order this if you can), and Pocky sticks for dessert. Sweets are not common to Japanese meals so you could end this with plenty of fresh and dried Asian fruits. Green tea should be the beverage of choice.
As for traditional games, the most fun (and easiest) would probably be karaoke! Give lots of prizes here, from the best singer/performer, to the most out of tune, funniest, softest, etc. Come up with the most categories possible. Everyone should win something here.
Favors could be a selection of Japanese snacks like savory rice
crackers, wasabi potato chips, and salty-sweet dried fish. Or, a
travel-sized Japanese toiletries paired with Onsen bath salts
packed into a miniature bamboo bucket would be perfect.