Well that escalated quickly.

[Penn Almasy]

kurl

How many EIs does that make Mephiste be referenced in? I wonder where all that's going.... since it seemed it was defeated in the newest Rose Saga thing

Seems being the keyword here.

Mephiste has most likely been sealed away.

Mereluna

I would like for Mephiste to return to ******** things up after getting dumped by a high schooler. >____>;

More like "that's what you get for trying to NTR a legendary princess away from her paladin."

[CioccoLatte]

Penn Almasy

They simply need a good writer to flesh out Mephiste in full. The poses only need to correspond to that.

Or was it the other way around?

I think this chicken-egg question was asked to an artist before...and I think they replied with "both". Sometimes they start with the story-concept first, then create the items after...and sometimes the ideas for items/outfit-ensemble come first and only then is a story created for it.
I don't know which would work better for a Mephiste REI though...