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.
Taking place directly after Thunder Force III, the ORN Empire is thought to be defeated by the Galaxy Federation, but still suffers from increasingly frequent attacks from hostile forces. The forces are discovered to be the "Vios", an army made up of allies and residual forces of ORN. The Galaxy Federation discovers the location of their headquarters on the planet Aceria and attacks, but since the power of Vios has grown greater than the previous ORN Empire, the Galaxy Federation forces are initially defeated. Once again, they develop a new small yet powerful fighter spacecraft, the Fire LEO-04 "Rynex" to eliminate Vios. The player controls Rynex and travels through ten stages while battling Vios forces.
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 the exact 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 CLAWs. When the ship is not firing any weapons, a charging noise is heard (followed by a chime when fully charged) and the CLAWs 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.
The soundtrack of the game includes atmospheric synthesized scores, while hard-rock with backing synths take a roll in the boss sections of the game. It is especially notable as being varied and intense, greatly enhancing certain moments of gameplay, such as the spectacular battle with huge mechanical boss above the Strite Sea, or the entrance of the player's nemesis, an enormous and seemingly indestructible robot.
Completing the game unlocks ten bonus (omake) tracks in the BGM player in the options.
Thunder Force IV had a more sophisticated regional lockout chip than most Mega Drive games, meaning that you could not play the Japanese version on a European Mega Drive, and vice versa, with a Bridge Adapter. However, a Mega Key adapter or a Game Genie would enable you to do so. Thunder Force IV also has the distinction of being one of the only European Mega Drive games to have been properly optimised for PAL televisions, meaning that it ran at the correct speed, unlike most games which ran 16.7% slower than their NTSC counterparts due to sloppy conversion between TV systems. The game still featured black borders however.
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.
Setting 'lives' in 'options mode' to zero on the PAL & NTSC-U/C versions gives 99 lives per continue.
Pause the game and enter Up, Right, A, Down, Right, A, C, Left, Up, B, Up to be granted all weapons. For CLAW/Thunder CLAW , press the Right button at the end of the aforementioned code sequence.