Basic Outline (will be fleshed out later)
Quincy are a group of humans that train to manipulate their Reiryoku and that within the Reishi around them to expert levels.
Each quincy learns to channel Reiryoku in some form of projectile, most frequently a bow, although pretty much anything is possible.
A Mekkyaku, or Quincy Cross, is some form of symbolic artifact (such as a cross, pentacle, etc) used to focus their power, without it, a Quincy is notably weaker (-1 to Spiritual Velocity and Spirit vs Resistance for purposes of just about anything they can do, with the sole exclusion of Ginto.)