It's not necessary to have a license to guide in pairs. All you need is the sound mind to enjoy traveling with guests.
However, the guests are eager for their long awaited travel in Japan. Through preliminary consultation on the web page and guiding, you will be required to have a kind heart and sufficient english skills. It's important to tell your strength and weakness at an early stage, so that they can understand you well and get reach to the real you. For example, let them know you are not good at English, history, and etc. which helps you keep away from the troubles and misunderstanding. This will make sure you will have fun with each other.