This is a long shot but you never know... My Grandfather was John Stephenson born 1930, Durham. He was injured during the Korean war and met a Japanese woman, we don't know her name but according to my Nanna they had a daughter in the early 1950's that was either called Kim or was nicknamed Kim. When he returned to the UK he wasn't allowed to bring his girlfriend and the baby back with him and by 1957 he was engaged to my Nanna.
That is as much as I know but one of John's granddaughters was approached over 10 years ago by a girl claiming to be his granddaughter too through his first relationship before he met my Nanna but nothing more came from it and I only found this out not long ago. So we now believe that Kim and her own family may be living in the area.
He passed away in 1991 and had seven children with my Nanna, the oldest born in 1957 and the youngest born in 1967 who all would be interested in hearing about their older half sister. He went by many nick names which included Jackie, Danny and Darky but also used other names over the years (sometimes refusing to tell people his real name)
If this sounds like it could be you or your family then please don't hesitate to get in touch. Also remember everything I know is second hand and some of this may be slightly or very different from the actual truth.