I have a sister, but I've only met her twice, and that was 24 years ago.
My Mum had my sister when Mum was in her late teens, and gave the child up for adoption. I didn't ask why but I assume there were a bunch of good reasons. My Dad wasn't in the picture and wouldn't be for half a decade.
After my parents married, they had me and my brother.
When I was 14, my Dad took me and my brother for a drive, and gave us some news.
1. We had a 21-year-old older sister.
2. No-one in Mum's family knew about it except for her mother.
3. My sister had contacted Mum and wanted to meet her.
4. My sister was at our house, meeting my Mum, and we were going home to meet her, too.
I remember walking in and giving her a hug. I can say that my sister was a nice young woman, and must have taken after her father in looks because she didn't resemble my Mum at all, but not much else about her stayed in my memory. She had been adopted by a upper middle class couple who couldn't have kids of their own. She was a nurse and was joining the Navy.
We met my sister one more time a short time after, when we were invited to her mother's home. I remember her adoptive mother was polite, older than my parents, and just a bit snobby.
Some time later Dad said that Mum got a phone call from the adoptive mother. They wanted to carry on living their lives as they were and didn't want any more contact with us.
I never really knew how Mum felt about all this, and I've never figured out a good way to raise the subject. From the little I understand, she was quite hurt by the rejection, and it never seemed like a good idea to raise the subject again. If my sister had never contacted Mum than I suspect I never would have learned of her existence; Mum would have preferred not to relive the trauma.
I occasionally think about her and wonder what she did with her life. Never had any success finding her online.
About 10 years ago I did 23&Me. About once a year since then I check to see if I have any close relatives that I never knew about, and every year there are new DNA relatives, but I share typically less than 1%, so, not close, not that interesting. Fourth cousins, no recognizable last names.
Two years ago in 2022 I did my annual check expecting no one close but this time there is a first cousin, an anonymous person listed only as "Ann B". We share grandparents, we share 10% the same DNA profile. Her profile shows that she is 50% Japanese. I immediately send an email to her, saying hello. An entire year goes by and in 2023 I get a response that is only: "Ho, is Judy your mother?" I write back immediately saying yes. I also tell her that my Mom, Judy, has just passed away, and I send more information telling her that I have two siblings so counting me she has 3 new first cousins. And I ask, how are we related? No answers. None.
In my family somewhere I am either missing an Aunt or Uncle (Ann B's parent) or my only Uncle (Judy's brother) had a child with someone other than his wife. Uncle "Bob" wasn't in the military nor ever traveled to Japan as far as I know, but Uncle Bob did have an uncle that lived in Hawaii. Uncle Bob had 5 children with Aunt J, there are my only cousins (until Ann B). I haven't asked any of them about Ann B.