So is this a "Masters of the 4th Grail War summon the Servants of the 5th" scenario or does chibi Rin somehow have EMIYA as her Servant, because this scenario should be damn near impossible if it's the former. Gilgamesh basically goaded Kirei into giving in to his evil urges and then encouraged him to betray Tokiomi. If Tokiomi somehow had EMIYA as his Servant instead then Kirei would have most likely remained obedient.