Onigiri is a very popular snack in Japan. I ate it for breakfast every morning during my time in Japan. You can read a post I wrote about breakfast here. For someone who is new to this wonderful treat, the following steps explain how to open and enjoy this snack without creating a mess.
The onigiri wrapper will have 3 steps listed somewhere on the pack. Try to find it. It will look something like the image below
Step 1: Open the wrapper by tearing a thin film as shown below
Step 2: Hold one side firmly (but not too tightly) while carefully pulling out the other edge (normally right side) as shown below
Step 3: Slowly pull out the remaining piece of wrapper. Sometimes, this last piece of wrapper is stuck to the green seaweed. Hence, be careful so as not to pull the seaweed along with the wrapper.
ENJOY! or as they say in Japanese, Itadakimasu!