Shurikens are typically fast (AGI normally 10-20), have low physical damage, higher magic damage, and are low at MP. Kunais are slow (AGI normally 30-40), bigger damage, inferior magic damage, and pierces enemies (but not walls) at a certain chance for each enemy that gets caught in its range. Note that attempting to put a Piercing Card compo into the any kunai will NOT improve the enemy piercing rate.