Space Invaders is the genesis of arcades as we know them. Without Taito's immortal single-screen shooter, it would have taken longer for games to be recognized as a full-blown industry instead of hobbyist toys. While Pong boosted game recognition worldwide, Space Invaders caused the game market to skyrocket. It was such a simple idea too: A mobile gun zaps waves of incoming aliens who return fire and move faster as you file down their ranks. They weren't originally supposed to increase speed to compensate for their lost soldiers, but this computing error exponentially increased its challenge and made it a more fascinating game than anybody expected it to be. So with its massive success, it would only be expected to have a legion of imitators following in its tracks. And oh my land, were there imitators. Some releases didn't imitate so much as they... WERE Space Invaders, albeit under different names, with Konami's Space King being the most shameless of ripoffs (they had a long way to go until Gradius). The most successful Space Invader imitator, Namco's Galaga, further revolutionized arcade games, and even today, you may still find the errant Galaga machine in any given Pizza Hut restaurant (sometimes backed with Ms. Pac-Man). The next big step forward for shoot-em-ups, Xevious, was also by Namco, but even as games started to rip that game off, there was still a place for the old style single-screen shooter, even all the way up into 1985. That brings us to Repulse by Sega, which is perhaps one of the more entertaining yet lesser-known "Invaderlikes" out there.
Repulse starts off with a brief story of fairly mangled English set in A.D. 1999 (which seemed like "the future" from 1985). The following is preserved with all appropriate inappropriate grammar: "The great nation of "Aquila", conquers of the universe, now face of Earth; their final conquest. The battle with the mighty "Aquila"... The time has come." So you're fighting against an evil alien force named Aquila and you're not about to let Earth buckle to a bunch of intergalactic jerks. Starting on the Moon before moving to various locales around Earth, Repulse features six levels with completely different backgrounds and increasingly aggressive enemies, and it actually does not loop over after you beat it. While the concept of levels are taken for granted nowadays, most games back then just kept looping until you ran out of lives. Shmups were starting to gain a bit more structure in the mid-eighties, where instead of just throwing out waves of enemies ad infinitum, there would be actual levels with unique backgrounds and enemies which led to an (often super-short) ending that may or may not have led to the game looping over after the end. Gradius was notable for said structure, with seven levels leading to its infamously anticlimactic finale. Repulse is also an early shooter to adopt this format, though the actual backgrounds where you fight matter less than the waves of enemies you face.
Repulse employs an interesting pseudo-3D perspective which makes it seem like you're shooting enemies in front of and above you at the same time. You can move upward to about a fourth of the screen, and the view pans slightly if you move horizontally. Your craft is a slick white-and-red anti-air fighter armed with a fast-firing laser and a shield system. Instead of those clunky old physical shields, you instead get an energy meter that powers your ship's own force field. Each hit you take while the shield is active drains your shield faster, but it's better than getting hit without shields active! The enemies you face start out with your basic fighters which fly into the background before zooming back up to the foreground while firing flashing bullets in your general direction. Then you have rocket ships that divebomb you, UFOs which warp in from thin air, indestructible mirrors, submarines that pop out from water and spray bullets, spider robots which shoot and shuffle, and a fair variety of other enemies which become more exotic and vicious as you travel farther into the game.
Not everything flying in front of you is bad, and a friendly helicopter may show up, but it is a bad idea to destroy it. If you temper your itchy trigger finger and avoid hitting the helicopter, it bestows upon you a power-up which boosts your shield gauge to full and fine-tunes your gun to allow automatic rapid fire. If you hit it and blow your power-up chance, it can further detriment you by the heli-wreckage somewhat humorously falling on your ship and obliterating it. With any luck, you'll get to hold onto your boosted power until the end of the level. At the end of the first stage, you just face a slightly rougher-than-usual rush of enemies, but all stages after that present you with a boss. Levels two and three have you fight a giant enemy warship, but level four presents you with an even more titanic mothership, which only stays on-screen for a few seconds and is mostly there for bonus points; you then fight this mothership proper for the fifth and sixth level. The bosses throw barrages of projectiles at you while many enemy fighters swarm about to defend their base; careful maneuvering and timely shield use is key to victory.
Repulse is as simple as it is solid. It looks great for the time with the 3D effects and its minimalist sound design (lots of firing sounds with music only chiming in for the ominous boss theme) fits the alien invader mood of the backgrounds. It plays fast, hits hard, and is everything that you'd expect for a shmup around that time.
When looking at the developer's pedigree, it's easy to see why this is a fine shooter. The company who made this game was known as Crux, and they only made one other game under Taito called Gyrodine, but Crux was also founded upon the ashes of another company named Orca, which also made two shoot-em-ups called Espial and Zodiack. Crux plopped in the midst of developing Repulse, and the game apparently ended up being finished at Kyugo, as that's who Sega identified as the game's developer, and there's also a version of the game with the Kyugo logo named 99: The Last War. Many of the staff members eventually re-reformed under the name Toaplan, a company synonymous with high-quality shooters and are best known for the bad English-laden Zero Wing. Toaplan also defaulted sometime in the mid-nineties but had broken off into four other companies: CAVE (perhaps the only dedicated shmup company today, and somewhat infamous due to their bullet hell shooters and recent affinity for moe aesthetics), Raizing/8ing (shmup masters and the creators of Bloody Roar, who would go on to help with Tatsunoko vs. Capcom and Marvel vs. Capcom 3), and the lesser known Takumi and Gazelle. Shooting has always been in Crux's blood and it carried along to all of its future incarnations, but Repulse serves as a nice reference point for humble beginnings.