Neesa is a boss from Vagrant Story. A commander of the Order of the Crimson Blades, she attacks the player along with Tieger in the Undercity.
You only have to beat either Neesa or Tieger to win. After one is defeated, no stat roulette or treasure is rewarded.
Equipping weapons strong against Humans works well in the fight. Offensively, there's little to be done aside from buffing yourself, and casting Tarnish on them.