Since you're starting out, I would recommend looking into a image manipulation program like Photoshop to be able to adjust the whites in pages so when you go to erase the japanese text, you don't leave a big noticeable box in the bubble.
Also I would recommend looking into more appropriate fonts such as CC Jim Lee and Zap Raygun: using FULL CAP versions of fonts that can do upper and lower case characters are very aesthetically pleasing in general.