In Japan it's quite common for a grown man to adopt another grown man.
It started when company owners wanted to keep the company in their family but either didn't have sons who could inherit it, or didn't think their sons where up for the job. So what to do? Hand it over to their daughters? Ha! Don't be ridiculous! It's much more sensible to adopt a 50 years old man from work legally and keep the company in the family that way!
Gay weddings aren't allowed in Japan, so gay couples use this whole adoption business to become family in the eyes of the law. That way they can secure each other financially and be allowed to see each other in places where only family is allowed.