hey iam nepalese passport holder and now iam in japan for study and i want to visit my family in HK

You can just apply for a tourist entry permit to visit your family in HK. You should first prepare the relevant documents containing proof of your financial standing, the application form, a passport-style photo, copy of your passport, flight itinerary, accommodation arrangement, and an invitation letter from your family. And then ask your family to submit the application to HK immigration department to apply for it.