Research has led me to conclude this is probably the protagonist from Satou Kuuki's 聖晶希石エスフェール (Holy Crystal Esphére) novels, but I don't know her name.

machan12 said in comment #2585016:

Research has led me to conclude this is probably the protagonist from Satou Kuuki's 聖晶希石エスフェール (Holy Crystal Esphére) novels, but I don't know her name.

キスティアセレス立ち絵

this is the textless version of the cover illustration of comic unreal vol 91. it's found in the volume

@Philipnotech seems to be posting some image samples from ehg but at least this one has the full size (from ehg at least)