I think that Kuina’s mother was a Shimotsuki clan member that left Wano 23 years ago with an expedition to retrieve Shusui and Ryuma’s remains.
So let’s start with a little recap:
-A ship arrived from Wano to the East Blue “a few decades ago”. This is almost certainly the Shimotsuki Village where Zoro grew up. The village shares its name with the Wano clan that Yasuie and is part of, has a dojo, and the dojo’s uniforms resemble those of Yasuie’s retainers.
-“One of the descendants of someone on that ship is a person that everybody is familiar with…” but ” It isn’t going to be a major plot line, it will just be a minor story”. This makes people born in Shimotsuki village within the past 3 decades candidates to be the mentioned descendant.
-SBS and Vivre Cards claim that Zoro, Kuina and Koushiro are all originally from the East Blue. I will also add that Zoro is 21 currently, Kuina would be ~22, and Koushiro is 51. This eliminates Koushiro from being the mentioned descendant because he is too old. Personally, I think the “minor story” part eliminates Zoro.
-In chapter 0 (released with Strong World), we see Kuina’s mother alive in the East Blue 20 years ago when Kuina was a baby.
My conclusion: Kuina’s mother traveled from Wano to Shimotsuki Village before Kuina was born. There she met Koushiro, and had a child with him. Koushiro adopted Wano customs, and ran the dojo after his wife’s death.
Why did the ship set sail from Wano?
-In chapter 0 (released with Strong World) we see that the Shimotsuki village and dojo already exist when Kuina is a baby 20 years ago. And for Kuina to be born in the East Blue, the ship had to have left Wano at least 22 years ago, the earliest leaving time being about 23 years ago.
-Kaido invaded Wano 20 years ago, so unless a warning was issued (Prior raids, or a prophecy from Lady Toki), they did not leave as refugees.
-Moria stole Shusui and Ryuma’s corpse from Wano 23 years ago.
-The Shimotsuki clan share their family name with Ryuma and may be his descendents. Additionally, a member of the Shimotsuki clan was Daiymo of Ringo, which houses the Northern Cemetery where Ryuma had his grave.
My conclusion: The ship that left Wano may have been composed of Shimotsuki clan members seeking to retrieve Ryuma’s stolen sword and corpse.
*Theory by HungryNacht
