The Fifth Holy Grail War is already very messed up, but this version is even more so: all of the Servants are of the same class - Caster - except of course for Gilgamesh, who's left over from the Fourth. (This is why the subtitle says 'not to be taken seriously'.)
Any being that qualifies for the Caster class may be summoned, and if they try to summon a second Servant, they'll most likely botch it a little, as Medea did in canon. Of course, if Caster was a Master in a Holy Grail War in life, he or she might not botch it, or not as badly.
I wonder how Shirou would react to getting Counter-Guardian MATOU (Sakura), for example, or how EMIYA would react to being summoned as a Caster, instead of an Archer (if he qualifies, which he might not).
Any being that qualifies for the Caster class may be summoned, and if they try to summon a second Servant, they'll most likely botch it a little, as Medea did in canon. Of course, if Caster was a Master in a Holy Grail War in life, he or she might not botch it, or not as badly.
I wonder how Shirou would react to getting Counter-Guardian MATOU (Sakura), for example, or how EMIYA would react to being summoned as a Caster, instead of an Archer (if he qualifies, which he might not).