Source: Wikipedia, "Xain'd Sleena", available under the CC-BY-SA License.
The main character, Xain, is a galactic bounty-hunter who must defeat evil forces who oppress five different planets. The player can select the in any order to play the various planets, so, there is no 'official' sequence of play (For the U.S. version, this game was released as 'Solar Warrior'. This version goes through a set sequence instead of having to choose planets).
Each planet is played with right horizontal and vertical scrolling shooting enemies and dodging natural hazards. Xain can crouch, double crouch, jump and double jump. In some of the planets the player will need to kill a sub-boss to resume. Certain enemies carry a powerup which changes the default laser gun into a different weapon. The different weapons which are cycled through powerups include a laser-grenade gun, a 2-way gun, a spreadfire gun and a strong bullet gun with their own respective damage and direction firing capabilities.
At the end of the planet, the player is goes into battle with a boss. Once defeated, the player plants a bomb (to the boss's base) and has ten seconds jump into the into the starship.
The next half of the planet stage is an interlude stage during which the player must battle through waves of enemy ships while heading to the next planet. After three planets there is a battle through an asteroid field and against a giant mothership.
When all five planets are liberated, the player will be play a longer stage on a gigantic metallic fortress, facing bosses previously met along the way. Fighting bosses in this stage is optional. Halfway through the stage the player plants a bomb on the fortress core and has 60 seconds to reach the exit hangar and jump into the starship.