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Thunder Force IV is a side-scrolling shoot 'em up video game developed by Technosoft as the fourth installment of the Thunder Force series. It was released respectively in July and September 1992 for the Sega Mega Drive/Genesis console in Japan and the United States, and in December of the same year in Europe. In the USA, Sega of America decided to rename the game as Lightening Force: Quest for the Darkstar. In Europe the name was left as Thunder Force IV.
Gameplay
The game format is mostly unchanged from the previous game (horizontally oriented and forward scrolling). However, many of the stages now stretch beyond the height of a TV screen, which allow the player more space to maneuver and dodge incoming fire (but also makes it easier to miss power-ups). Also, the player now has the option choosing the play order of the first four stages, instead of just the starting stage like in Thunder Force III.
The weapon system is also similar to Thunder Force III. Featuring the same upgradeable defaults, and unique extra weapons that are either exclusive, or were in previous games. Again, upon ship destruction, the weapon currently being used is lost, apart from the defaults. The CLAWs return, and basically have exactly the same function as their Thunder Force III counterparts. The speed setting also returns, although it is represented by a percent gauge from twenty-five (lowest speed) to one-hundred (highest speed). Tapping the speed button will increase speed by 25 percent and holding it down will increase speed gradually by one percent.
The most significant addition to the ship arsenal is the Thunder Sword, a very powerful lightning-based frontal attack. At the game's halfway point, the ship receives an add-on part which enables the use of the Thunder Sword. From here, the one requirement of using the Thunder Sword is that the ship be equipped with CRAWs. When the ship is not firing any weapons, a charging noise is heard (followed by a chime when fully charged) and the CRAWs will appear to be surrounded with electricity. The next press of the fire button will discharge the Thunder Sword. The blast is stronger if charged longer and is at its strongest when fully charged.
It is possible to play two-player co-op using two pads simultaneously. One player can direct the craft and choose speed settings, while the other can fire and choose weapons strategies. Whether this was ever a proper feature is debatable, as there is no documentation for it. However, the fact that both joypad inputs can be used is unusual for a one-player game.
Source: Wikipedia