A third-person 3D shooter from the development team responsible for Jet Set Radio, Gunvalkyrie has players suiting up as one of two team members sent to the remote planet of Tir na Nog to rescue a missing scientist. Since each of the four areas of the planet is overrun with large insect-like aliens, both characters have been outfitted with special battle armor allowing them to hover in the air for a limited time and to propel themselves at high speeds using rocket boosters.
To help battle the aliens, characters come equipped with a maximum of three weapons, each of which can be further upgraded using points earned from completing missions. Kelly O'Lenmey uses a Heat Blaster, Drive Gun, or Plasma Hook, while Saburouta Mishima fires a Matchlock Cannon in addition to the Plasma Hook. The Plasma Hook can also be used as a climbing device once it's latched onto glowing orbs found at certain points in a level. Special attacks can be performed on the ground or in the air to wipe out multiple enemies at once, but these moves come at the expense of fuel.
A total of 15 missions are available as players advance through the planet, which involve eliminating all of the aliens in the area before being able to exit. An overhead map screen highlights the number and location of enemy targets as well as the passageways needed to continue to new areas. While battling the aliens, players can collect fuel and shield balls to perform more special attacks or absorb more damage, and boost combos can be used in midair to help regain fuel or charge-up the main weapon.
At the end of each mission, a rank and score will be assigned based on performance in the areas of enemies defeated, overall clear time, use of the boost technique, and finding one of the hidden Halley Cores on a stage (finding them all will increase the character's power). The points on the tally screen can then be used to upgrade armor as well as weapons, such as adding the ability to target multiple enemies at once or increasing the amount of damage caused by a specific armament