Time Slip

The game takes place in 2145, when the Tirmatians, intelligent alien beings from planet Tirmat, discover a sort of space-time portal -or "rift", as it is called in the game- that interconnects their homeworld with Earth. Meanwhile, human astronomers discover the same rift, but are not aware of the existence of Tirmat. They also discover that the rift is growing in a geometric rate. As they try to study it, the Tirmatians launch an exploratory probe, named "Torquemada II", in order to find a planet similar to Tirmat; the probe soon finds Earth and sends information back to Tirmat.[2]

As Earth astronomers continue studying the space-time rift in 2147, the Tirmat leadership agrees to send explorers to Earth. It turns out that Tirmatians are planning to conquest Earth to convert it into "Tirmat II." However, Tirmatians have learned that humans have highly developed fighting skills and a vast amount of weapons, and they obviously would not agree to be enslaved. Because the power of the human defense forces, they decide to change their strategy, abandoning a conventional, frontal attack on Earth forces (because they would likely face a high casualty rate and even a defeat) in favor of a plan focusing on a time-traveling technology. This plan consists in sending Tirmatian expeditionary forces to several historic ages, in order to interfere with the development of human weaponry. By doing this, they can secure a victory by truncating the evolution of human weapons, leaving humankind with nothing but weak weapons and at the mercy of Tirmatian forces in the future.[2] But their carefully planned strategy has a flaw: it failed to take in count the human intellect.

As Tirmat expeditionary forces are dispatched, a group of scientists led by Dr. Vincent Gilgamesh unveils the prototype of a time-travelling machine.[2] Suddenly, Tirmatians launch an attack on the laboratory where Dr. Gilgamesh works; all but Dr. Gilgamesh are killed. Without having time to test the time-traveling machine, he decides to travel back in time to stop Tirmat's conquest plans. A battle between Dr. Gilgamesh and Tirmatians starts, and it is only a matter of time to decide who shall win.

The gameplay is similar to that of Contra III: The Alien Wars. The player uses several weapons, such as laser guns and bombs, which are collected as the game progresses. However, weapons are lost after losing a life. It is also possible to use armored vehicles in some levels. The game's mechanic also features a TGS bar, or "power bar", which must be filled with special time crystals before emptying; otherwise, the player will lose a life each time the bar empties. The TGS bar is a part of the time-traveling device, and must be filled frequently. The bar slowly empties itself and by being hurt by an enemy, so players must literally "run for their lives" and collect as many crystals they can. After scoring a given number of points, players are awarded extra lives.

Levels contain enemies and traps; players may find themselves fending off many weak enemies before battling an oversized (albeit weak) sub-boss, only to face an even stronger, bigger level boss. Traps, in turn, are based on the technology available in each age. Sets of traps are scattered all over the game.