I am wondering if there are any job openings that offers Visa for an entry level Rails developer position.
Japanese companies traditionally divide their recruiting into two categories: university students and mid-career hires. “Entry level” or “Junior” positions still aren’t so common to see here generally. Furthermore, if you’re not based in Japan yet, companies are normally only willing to consider people who are exceptional matches, part of which is usually having professional experience with their tech stack.
This doesn’t mean it is impossible to get a job as a developer without professional experience, but it’s going to be challenging. I’d recommend looking for ways you can demonstrate your ability as a developer. For instance, having pull requests accepted to Rails or another major gem is a great way to demonstrate your coding abilities, and writing technical articles or giving presentations can demonstrate your communication skills.