I ask this because there seems to be difference of opinion about this. Specifically surrounding Fushigi Yuugi.

Fushigi Yuugi Gendou Kaiden takes place before Fushigi Yuugi chronologically some 70 years, Main character comes from the 1920s.
Fushigi Yuugi was written first however and the main character comes from the 1990s.

I've seen the 'Related Series' tags for these change quite a bit and was wondering if there was any right one we're suppost to use?
(personally I think Gendou should be prequel)

Currently the tags are
Fushigi Yuugi page
Related Series
Fushigi Yuugi Genbu Kaiden (Sequel)

Fushigi Yuugi Genbu Kaiden page
Related Series
Fushigi Yuugi (Prequel)

I was just wondering if the tags should be the other way around? Sorry if this was a waste of time, but it was bugging me.

You're correct to bring this to our attention.

However, when dealing with things like these, we go by publication date.

Hence, while chronologically speaking, Gaiden does come first, the original was published first.

We do this because often times a Gaiden story, while it does take place often in the past, harkens back to the original story somewhat.

If everyone read the Gaiden first, then the original story, it could be quite confusing.

That is why we go by publication date.

A person reading Fushigi Yuugi would be more inclined to read the Gaiden after finishing the original. Reading the other way may be a different story altogether.

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