Tracing siblings

My father may have fathered children in the 1960s in Yokohama or Tokyo - extra maritally but nevertheless, the children would of course be related to me. How do I find out? Is it likely that his (British) name would be on birth certificates and is there any way in which I could at least try to locate any possible siblings? My parents are both dead.

Also, I would love to show my own kids where I lived in the 60s in those cities. Any archived telephone directories from those days?

Thank you so much for any advice.

Have you taken a look at the Yokohama Navy Exchange thread? There is lots of useful information on there that might help you recall where you lived.

Rhiannon Thompson,

I think it depends on the situation. For example, I wonder what made you think you have half-siblings. Depending on your answer, it just might be easier asking information at major Japanese newspapers like Asahi, Yomiuri or Mainichi or Japan Times which all have English versions.

If you're trying to look into official documents, generally it depends on what nationality these children may be. For example, if you think they obtained British nationality through the British Counsel in Japan upon birth, you can probably start by asking British public halls such as a local city hall if you were in Britain.

Or for example, if the mother was Japanese, the children are most likely registered under their mother's official records (koseki). In that case, you need to at least know what city the mother lives in or lived in at the time of the children's birth, or what city the mother is originally from. Once you know that, you can try contacting the city hall of that city for more details. However, to protect the citizen's privacies, they may not be able to provide enough information to you. You just have to try.