Obtaining a working visa that lets you work as software engineer in Japan is relatively easy compared to other countries. It costs a company almost nothing to sponsor your visa, there aren't any quotas on the number of visas issued, and the requirements to qualify for a visa itself are low.
The most common visa for software engineers in Japan is the Engineer/Specialist in Humanities/International Services visa, which is trivial to obtain if you have a related university degree, such as a Bachelors of Computer Science or Software Engineering..:.