Reimu as a hoplite (Ancient Greek heavy infantry, those who held the line in battles), disciplined and sturdy (compared to the other three). Sanae as an axe(wo)man, Google translate gave 아그리사나에 as Agri-sana, so an Agrianian axewoman (Ancient Macedonian shock troops, those who aggressively attack enemies in battles), less restrained than the others (look at those eyes). Marisa as a slinger (those who pelted enemies with stone bullets to death regardless of how much armor they wore, much like David vs. Goliath), a reference to her ungodly laser-beam.
And Kyouko as a lowly Ancient Persian conscripted spearman, disdained in the ancient world as much as Kyouko is disdained as a lowly broom-carrying stage-2 boss.
