Crossovers that should not be: Reigning in (the) Chaos

[Jorlem]

And today started out as such a good day too.  I really should have expected this to happen sooner or later, but it still came as a complete surprise when Haruhi burst through the clubroom door as usual and shouted
"I've decided our activity for today! We're going to summon a demon!"
Anyway, one failed argument, chalk circle, and homemade incantation by Ultra-Summoner Haruhi later, the demon was standing before us.  If you can call him a demon.  This human-like 'demon' had neck length purple hair, a wooden staff  with a red ball inset near one end, and an expression that looked creepily similar to one I had seen on Koizumi's face.
Haruhi blinked, then pointed at the unfortunate person in her chalk circle, in what she must have thought of as a dramatic manner.
I am Suzumiya Haruhi, demon!  What is your name!"
The man in the circle's smile grew slightly wider.  Who is this guy, that this insanity doesn't even faze him?!
"I am the mysterious priest, Xellos."
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Stand between the Silver Crystal and the Golden Sea.
"Youngsters these days just have no appreciation for the magnificence of the legendary cucumber."  --Krityan Elder, Tales of Vesperia.