Subaru itself cited[1] Kojiki literature from the 8th century when talking about the origin of its name.

[1]: https://web.archive.org/web/20100411083646/http://www.subaru...

Unfortunately, trying to find anything more online, such as what exactly the Kojiki says about them, doesn't seem to yield much.

Chinese have a story called 天仙配, where a fairy maiden married to a mortal. That girl is called seventh fairy, as she’s the last of 7 sisters.

So it is very similar to the lost Pleiad, but the seventh fairy is taken back by her god father.

Doesn't look like. According to Japanese Wikipedia they used to be also called 六連星 ("group of 6 stars", I think?).