Which of the following relationships can lead to a living relative kidney transplant?

Hello, Kidney Friends!

Today we are going to tell you a love story:

A year ago, a friend of mine called me. Her brother Xiaoshuai fell in love with a girl named Xiaomei. Recently, Xiaomei was diagnosed with uremia (as our long-time readers know, kidney transplants are an effective treatment for end-stage renal failure) . Driven by love and watching Xiaomei languish, Xiaoshuai plans to donate his kidney to his girlfriend.