There are 10+ playable aircrafts with its own unique skills. In addition, crystals can be obtained after destroying the enemy and this helps the player to upgrade the player?s aircraft attack skill up to level 3. Once the unit is powered up, the overall performance and the appearance are enhanced giving players higher chances to survive on the stage. Secret units with massive power can be unlocked through achieving the quests and this makes easier to win the colossal bosses."