Irina, a slave of the galactic Kharlal Empire along with her ill father, hijacks one of the Kharlal Empire's cutting-edge Drainus ships, in order to stop the advance of the empire and bring her father home to Earth. Not making things easier is that her sister Layla is a commander of the Kharlal Empire's military, and Irina will do what it takes to rescue her as well...
The Drainus ship is capable of the usual shmup ship armaments of firing its indefinite-use main gun and Smart Bombs for when things get tough. It also has an absorb shield that, when used, allows the ship to make contact with the enemies' energy attacks and release the energy as a volley of homing lasers directed back at the enemy. It can also build up power-up capsules that can be spent to upgrade the ship's features and invest in new weaponry and other equipment; new equipment can be obtained and equipped by pausing the game, or between stages.
Not to be confused with Darius, though it does seem to be a pretty direct Homage thereto.
DRAINUS provides examples of the following:
- Anti-Grinding: Bosses and other "defeat to progress the game" enemies have time limits in Arcade mode; once the timer runs out, the fight will continue but no more points can be earned from them, aside from points from destroying them.
- Anti Idling: In Arcade mode, the customization pause menu has a 90-second time limit. Once the timer runs out, the game is forcibly unpaused. However, the "hard pause" menu, accessed by holding the pause button and which only has options to unpause or quit, has no time limit.
- Armor-Piercing Attack: Physical attacks, which are marked with red outlines, will ignore your ship's absorb barrier and damage you anyway.
- Arrange Mode: Clearing the game once unlocks Arcade mode (in addition to Ridiculous difficulty). All story elements are removed, the player must start from Stage 1 every time and the player can only do a customization pause once per stage (although the player can still do a hard pause and quit the game by holding down the pause button). Three difficulty levels are available for Arcade mode: Normal (1 loop, equal to non-Arcade Hard), Hard (1 loop, equal to non-Arcade Ridiculous), and Extended (Normal but with 2 loops). On Normal and Hard difficulties, most upgrades that would otherwise be locked off until the 2nd loop are made available despite there being only one loop.
- Bad Future: Irina's copilot Gehnie hails from one where the Kharlal Empire dominated the known universe. Izumo is also aware of this future and keeps going back in time to ensure it comes about.
- Big Damn Heroes: At the end of the game, Layla arrives at the last second, having broken out of prison, to contribute her absorb shield to deflecting Izumo's final attack while Irina is struggling with her shield. When Izumo tries to perform a time jump once again, he realizes the device for it is missing and that Layla had pickpocketed it in advance. Irina and Layla release a counterattack that destroys Izumo once and for all, earning a happy ending for themselves and their ill father.
- Butterfly of Doom:
- In the second loop, Gehnie warns Irina that going back in time causes "the Chaos", in which even slight differences from the original timeline can have a drastic effect on the new timeline.Irina: We were supposed to have gone back in time, but enemy attacks and stuff... It all feels much rougher than before...
Gehnie: Yeah, that's what's known as the "Chaos"...
Irina: Chaos...?
Gehnie: When going back in time, even if you do everything almost exactly the same, a slightly new, different future is created. It's actually what I had feared the most... Things shouldn't change too drastically, but...
Gehnie: S-so... The chances I can save Layla are...?
Gehnie: I don't know... It's possible that an even worse future than before awaits us now.
Irina: Wh-what...
Gehnie: We've gone back in time, with the Drainus. So that means, this Drainus is even more powerful than the first time... Maybe the Kharlal Empire, seeing our armaments, has bulked up their forces as well. - In the end, it turns out to be a subversion. Governor-General Izumo had also gone back in time upon his defeat in stage 1-6, which is the real reason why the enemy forces are stronger. With his knowledge of the future, he's better able to prepare his forces. One Recorder conversation implies he's already done this cycle at least once before.
- In the second loop, Gehnie warns Irina that going back in time causes "the Chaos", in which even slight differences from the original timeline can have a drastic effect on the new timeline.
- Color-Coded for Your Convenience: Energy shots and lasers, which can be absorbed, are colored purple, while physical attacks, which cannot be absorbed, have crimson outlines.
- Deadly Walls: Colliding with walls, no matter how gently, will damage your ship. Easy and Normal mode have optional Stealth Bumpers that can be installed at the start of the game; these will protect your ship from terrain collision, but you will be unable to move through walls even during Mercy Invincibility.
- Gameplay and Story Integration: Why are the enemies more difficult in the second loop? Turns out that General Izumo had also gone back in time, to a point earlier than what Irina went to, thus allowing him to better prepare his forces.
- Giant Space Flea from Nowhere: The boss of Stage 5 isn't a Kharlal battleship, but rather a bizarre shape-shifting... thing that resembles a monolith. Gehnie hypothesizes it's a dimensional traveler.
- The Greatest Story Never Told: Discussed in the final Recorder, where Gehnie's commanding officer from his time explains that when he returns after defeating the Kharlal Empire, she and the rest of the council will forget that they ever sent him on the mission, since in the new future, it won't be necessary anymore.
- Harder Than Hard: After clearing once on any of the three initially-available difficulties (Easy, Normal, Hard), you unlock Ridiculous difficulty (in addition to Arcade mode), with the description warning that "no claims of difficulty will be entertained." Not only are enemy attacks stronger and denser, with enemies making more generous use of physical attacks, instead of your ship losing a powerup when getting hit and only getting destroyed if you get hit with no powerups left, you simply die unless you have a shield powerup that can take the hit.
- Heroic Sacrifice:
- At the end of stage 1-6, Layla takes an attack from General Izumo that was meant for Irina, having pulled a Heel–Face Turn at the last minute. She tells Irina not to fret and to take care of their father, but Irina won't have it, feeling that Layla wouldn't have had to die if she didn't hesitate to kill Izumo, and rewinds time with Gehnie's help to secure a timeline where Layla won't have to die fighting him.
- Stage 2-6 ends with Layla and Irina surviving Izumo's final assault and destroying him once and for all, but Gehnie, who had been helping them overthrow the Kharlal Empire, begins to fade from existence because the whole reason for his existence was to prevent the Empire from rising in the past, and now the Delayed Ripple Effect of creating a future where the Kharlal Empire doesn't exist has caught up to him. Layla and Irina are briefly heartbroken, but Gehnie reassures them that he had accomplished what he had set out to do, and tells the two sisters not to fight amongst themselves anymore.
- Justified Tutorial: The tutorial appears to be an in-universe crash course in piloting the Drainus, taught by Commander Layla, who assumes she's training just another cadet...until word gets out that she's been training the person who hijacked one of the Drainus fighters (Irina), and threatens to search and destroy her.
- Manipulative Bastard: One Recorder conversation reveals the reason Layla joined the Kharlal Army: She had pickpocked Governor-General Izumo's wallet. Impressed by her feat, he offers her a position in the army with the promise of a good salary. Paraphrasing: "You sure you want to stay a slave and never get out of that life?"
- Menu Time Lockout: While paused, you can freely change or upgrade your equipment, and then unpause; from a hypothetical outside observer's standpoint, your ship instantly changes its armaments.
- Mirror Boss: Just before the Stage 5 endboss, you encounter enemy Drainus fighters who can all perform attack-absorption counterattacks just like you can. Good thing you can absorb those in turn.
- Nice Job Breaking It, Hero: In the second loop, Gehnie believes Irina is doing this by having different words with Layla from the first time around, and tries repeatedly to warn her not to do so as doing so can drastically alter the new timeline. Ultimately, it's a subversion, as Izumo had also gone back in time to better prepare his army, and Irina was really speaking to a holographic projection of Layla all along while the real Layla was imprisoned sometime before the point that Irina jumped back to.
- One-Hit-Point Wonder: On Ridiculous difficulty, as well as Arcade mode on Hard difficulty, all hits will destroy your ship, when normally they would only take a power-up away and only kill you if you have no power-ups left.
- Plot Device: The "polycore" cores seen on most bosses. Destroying all six polycores in the present is Gehnie's objective in order to prevent a Bad Future where the Kharlal Empire is more readily able to mass-produce them.
- Power-Up: Collecting the circular tokens that some enemies leave behind will power up the lowest unlit power-up slot. You can customize what slots hold what power-ups in the pause menu. Taking damage will take away a power-up, and if you are hit with no power-ups, you will lose a life.
- Reactor Boss: Stages 4 and 6 have mini-bosses taking place in a reactor. Stage 4's is a guarded polycore, while Stage 6 is some other flavor of reactor.
- Redemption Equals Death: At the end of Stage 1-6, Layla turns against Izumo at the last minute and takes the attack that was meant for Irina, sacrificing her life as a result. When a distraught Irina rewinds time and makes it to the same stage in the new timeline, Layla averts this by absorb-shielding her Drainus fighter along with Irina's to shoot Izumo's attack back at him safely; both sisters survive and land on Earth to finally get their father cured of his illness.
- Shout-Out: The Stage 5 boss is made up of a bunch of blue cubes that can split apart, cross the screen, then re-form. Said cubes and the pattern they move in are clearly inspired by the "Cube Rush" segment of Gradius III.
- Slasher Smile: Governor-General Izumo sports a perpetual toothy smirk on his face, only ever faltering in Stage 2-6 when he's defeated for good.
- Take That, Audience!: The pilot of the Stage 3 boss, Manson, is an unattractive and portly man with a blatant crush on Layla, a clear jab at otaku who make "waifus" of female characters they obsess over, which is likely some players of the game.
- Taking You with Me: On the first loop, Irina and Gehnie think Izumo is planning to do this. In reality, he's just using his time jumper to escape to the past, and he's offended that anyone would suggest he would do something so petty.
- The Unfought: Despite being one of the antagonists for most of the game, Layla is never fought at any point. When Irina is made to fight what appears to be Layla by General Izumo in Stage 2-6 and defeats her, it turns out the Layla she fought is actually a hologram and the real Layla is in prison...or so Izumo thinks until a few minutes later.
