Back in 2003, Konami released Boktai, an innovative GBA title from Hideo Kojima, creator of the Metal Gear series. The game featured a solar sensor, requiring gamers to go outside and collect sunlight to recharge their weapons or finish off vampires. The game spawned two sequels on GBA (one which was never released outside Japan), and the series also had some crossover elements with the Mega Man Battle Network games. Now that the fourth game has come to the DS, it's undergone a rebranding in western markets, but the experience should be familiar to Boktai fans.

Lunar Knights is set in the distant future with two all-new characters. You start as Lucian, a mysterious vampire hunter who's out for revenge. In the second chapter, you meet Aaron, who's part of an underground resistance force fighting the vampires who now rule over the world. Eventually the two meet up and travel together, allowing you to switch between them at any time.

The game plays like a dungeon-crawling action RPG. There's no overworld to connect locations. Instead, you navigate a map and click on a town or a dungeon. Towns are completely menu-based. You simply click on the name of the shop or the person you want to talk with. Dungeons are presented in a top-down isometric view, and since the paths are all laid out diagonally, there are options to change to isometric controls on the cross-pad as well. I found it easier to stick with standard controls, but you may need to switch control styles in areas that force you to move across floating platforms. If you fall into the abyss, it's an instant game over, and you have to spend a couple hundred bucks in game money to continue from the entrance of the room.

Battles take place in real-time. Lucian uses bladed weapons like swords, spears, and scythes while Aaron uses an assortment of guns, including flame throwers and grenade launchers. This makes Lucian stronger in close combat, while Aaron is more effective firing from a distance. The battle system is rather deep. You can lock-on to enemies with the R button (a huge help in an isometric game), dash away, or guard with a shield by pressing B. Guarding at just the right moment can stun an enemy so you can counterattack. Beyond that, enemies all have elemental weaknesses, and there are advanced techniques like dashing attacks and guard cancels. You can even blow into the mic to whistle and distract the enemy, which is handy when you want to get in the first shot or avoid combat.

Another main difference between the two characters is that they draw their energy from different sources. Aaron can only recharge his weapons with sunlight, and Lucian can only recharge his with moonlight, but this doesn't mean that you have to play under a full moon. Instead of relying on a solar sensor, Lunar Knights features an in-game day/night cycle which you can monitor on the upper screen. Plus, even when Lucian is completely out of energy, he can still use his weapons; they just don’t do as much damage. For fans that do have a copy of Boktai or Boktai 2, you can plug the games into the GBA slot and use the solar sensor to "catch" sunlight and boost the in-game meter for a short period of time.

In previous Boktai games, you would journey through a dungeon, defeat a vampire, and then drag the vampire's coffin back through the level to purify him in the sunlight outside. Now the vampires have taken advantage of alien technologies to protect themselves from the sun. First is the hilariously named ParaSOL, which is a device above the planet that allows the vampires to block out the sun's rays and control the climate. Second is casket armor, which draws on the power of elemental creatures known as terrennials and shields the vampire from ordinary sunlight. So, in order to vaporize a vampire and gain the aid of its captured terrennial, you'll need to take its body where the suns rays are strongest – outer space.

You fly your opponent's body to a space station that uses concentrated sunlight to destroy the vampires, but to reach the station, you have to battle your way through 3D shooter stages that are somewhat similar to Star Fox. The ship is controlled entirely by touch – touching the ship and dragging the stylus allows you to dodge and you tap at enemies to fire your weapons. Since it's impossible to fire and dodge at the same time, it can be a little tough to get used to, and even then it requires some quick decision making to keep from being hammered.

The shooter stages aren't overly difficult, but they do offer a fair challenge since there are no checkpoints along the way. If you get to the boss and he takes you out with his mega-giant lasers, you'll have to start the whole level over again. On top of that, the final stage doesn't have any health pick-ups, making it absolutely necessary to learn the boss's attack patterns.

After you purify a vampire, you'll gain a new terrennial. These elemental sprites include the two that Lucian and Aaron begin with – the dark cat named Nero and the sunflower named Toasty. Each terrennial is aligned with a different element such as fire, ice, wind, or earth and changes the alignment of your weapon accordingly. Holding L pauses the game and allows you to quickly swap between weapons and terrennials. You also have a trance meter, which fills up to give you access to special attacks. Toasty and Nero join with your character to make you super-powerful for a short amount of time, while the other terrennials simply allow you to attack all the enemies on-screen at once by throwing fireballs, causing earthquakes, etc. Unfortunately, I think these trance attacks really cheapen the experience. If you're struggling against a boss, it's just far too easy to go into trance mode and knock him out without bothering to perfect a strategy.

Terrennials are also key to opening up extra areas in dungeons that often hide new items and weapons. Some areas are simply blocked by elemental cubes that can only be destroyed with an attack from an opposing element. Other areas can only be entered under certain weather conditions. Along with the day/night cycles that you monitor on the upper screen, you can also see changes in humidity, wind speed, and temperature. Higher humidity can cause plants to grow and build bridges. High winds allow you to ride gliders across gaps. Hot weather may dry up a lake with a chest at the bottom. Any area sensitive to weather has a handy weather statue standing next to it that turns red when the conditions are favorable. Each terrennial you gain unlocks a new climate setting on the ParaSOL. It's a cool idea that gives incentive to replay dungeons. The down side is that you can only change climate settings from the scientist's house, which means that if you come across one of these areas, you have to exit the dungeon, change the climate, re-enter, and find your way back to that spot.

If you talk to the right people in the towns, you can also unlock a number of side quests. These are all simple objectives like rushing through a level within a time limit or killing all the enemies in a dungeon. Most of the rewards aren't that big of a deal, but you can snag some extra cash and junk parts that can be used to power up your weapons.

Overall, Lunar Knights turns out to be a pretty fun experience. There's a good balance between the action and RPG elements, and the subtle depth of the battle system is aided by quick weapon selection. Plus, the final dungeon shows that the new dual-character system has some potential for cooperative play in the future.