An Angel For Fun

Saitama is a Guardian Angel that is assigned to protect a little boy named Genos. He claims that his job as a Guardian is just for fun, but as Genos begins to grow up... Saitama's outlook changes. He's suddenly much more serious about the safety of this mortal man.
Genos is a growing child. He's blonde and tan, and has a great family. He has a wonderful imaginary friend named Sai, and his life is perfect. Until he starts growing up. He grows out of the 'imaginary friend' phase and hits puberty, and his parents are always at work... He feels so alone.

Now, how can I screw this up for them?