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In this drama, there is a relation, which is described in the diagram below, between the characters.
In this drama, the characters have a relation described in the diagram below.

Are they both correct and do they mean the same?

Thanks.
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I would use "described by", but otherwise, they are OK and mean the same. The second is much easier to understand.
You can phrase it like this, too:

In this drama, there is a relation between the characters, described by the diagram below.
Comments  
Got it!
Thank you so much, Alphecca.
AlpheccaStarsIn this drama, there is a relation between the characters, described by the diagram below.