Mixed race

My dad's father was gaijin and dad's mother was japanese. He looks more western than japanese.
As other nikkeis, dad was proud to be japanese and he had never told me his western side since childhood.
When I was around 12 years old, I was always asking mommy: "I can't believe dad is japanese because he doesn't look so". Mommy replied: "You are right. He is mixed race. His real dad was a gaijin but don't tell dad that you already know it because he doesn't like to talk about that". I obeyed her. Besides, I saw dad lying about his identity to other people claiming he was a pure race, with a pure japanese blood. Perhaps, he was hiding his identity to me and I let it go.
My surname is japanese but it had to be a normal brazilian surname. My grand mother married again to a nikkei who registered dad as his son. At that time, it was common to register a child after many years its birth; so dad was not even registered when grand mother married again.
Today something different happened.
Dad called me and began to talk in a low voice. He doesn't trust my sister in law. He showed me some kind of gravestone but it would be better to say a grave wooden with some kanjis (chinese characters) in one side and a woman name with her birth and death dates. Her birth date was in 1938 and her death in 1939. The kanjis are used in Buddhist ceremonies. This baby was in fact my dad's sister from his father. She had the brazilian surname I should have. Finally, dad told me something about his childhood. Why so much secret for so long time?
I couldn't stop thinking about it.
Contrary to dad, I really want that my children understand my soul, my thoughts so that they don't misjudge me.
Coming back home, I told my older son what happened and I asked him: would you like to have a brazilian surname? His face is really japanese (his blood is around 90% japanese). He told me it would be really strange for him to have a brazilian surname. At dinner, my son asked me: How did your dad get this grave-wooden? Good question. I am so used not to ask questions about my father childhood that I didn't ask anything. Dad told me today that his grand father gave it to him; but then, I began to ask: he was just 3 years old when his sister died; so how come his grand father gave it to him? Was it really some kind of grave wooden? No, dad told me something about it. It was not to stay in the grave (wooden is a fragile material). I understood it was some kind of memorial to stay inside home.
I asked my son: why my dad did decide to tell me this today? and I tried to answer it:
- because he is really alone and facing death. Mommy is with Alzheimer and he is continually listening to that strange music that reminds him about his own mortality. He wanted very much to discover what was written in kanji and he was trying to find a way to decipher it. I really don't know what made him tell me this. Was his quest in discovering some hidden secret in the kanjis or was his strange way to tell me what my surname should be?
My own origin seems a lot of random events outside of anyone's control. My real gaijin grand father has never known me but his DNA is in me. I believe that the Lord elected me to be his own before the big bang; so He was in control of my origin. He has been writing my own story much before I was even born.