Seihou

This tale is set on Earth, far in the future...

Seihou Project (西方, where "Seihou" means West or Western) is a series of Doujinshi Bullet Hell Shoot 'Em Up games, developed by Amusement Makers. Known primarily as the sister series to the massively popular Touhou Project, the Seihou Project puts an emphasis on memorization and reflexes by focusing on less numerous but faster bullets compared to its sibling series. Notably, ZUN, the creator of Touhou, was involved in the creation of the first two Seihou games as a member of Amusement Makers, as its BGM composer.

In a distant future, Earth has fallen into near ruin after its natural resources are depleted, leading to the destruction of the environment and the extinction of nearly all vegetation on the planet. Driven to the brink of destruction, humanity finds its sole hope in the only surviving genus of plants left on Earth: the cactus. Erich, the chairman and founder of Cactus Company, heads the research to extract energy from cacti, discovering a miracle energy thus named Saboten Energy. However, while possessing power beyond even atomic energy, Saboten also proves to be extremely difficult and dangerous to control, causing large-scale accidents and nearly pushing Cactus Company to the verge of annihilation. Decades later, the Cactus Company manages to perfect the use of Saboten Energy, using it to slowly restore the environment, allowing humanity to bounce back.

The Seihou games chronicle the adventures of VIVIT, a maid-type combat android powered by Saboten energy, as she goes on errands given to her by her master Erich. She is later joined by Hirano Sakurasaki, a Miko who serves as the secondary playable heroine in Banshiryuu.

There are currently three games in the Seihou series, which include:

SH 01 Shuusou Gyoku
SH 02 Kioh Gyoku
SH 03 Banshiryuu

Although not officially connected, Samidare is regarded as a Spiritual Successor to the Seihou series.

Tropes used in Seihou include:

After the End: And humanity managed to rebuild itself.
Amazing Technicolor Battlefield: The final stage of Shuusou Gyoku, which apparently takes place in a dimension of non-physical concepts.
Batman Can Breathe in Space: Stage 5 of Banshiryuu takes place in outer space, despite the player characters not being in a spacesuit or vehicle of any kind. It's justified for VIVIT, who is an android, but Hirano...
Beam Spam: Erich is infamous for his infuriating use of homing lasers. It goes double for your opponent if you play as him.
Boss Rush: The extra stage of Banshiryuu has you fighting all the characters from Kioh Gyoku, one after another, culminating in a battle against Icarus.
Brutal Bonus Level
Bullet Hell
The Cameo: Marisa and Reimu appear as Bonus Bosses in the extra stage of Shuusou Gyoku. Yuuka Kazami appears as an unlockable player character in Kioh Gyoku. VIVIT herself (along with Gates) appears as the Bonus Boss of Samidare's Extra Stage (which also features Mai and Yuki as mini-bosses.)
Child Soldiers: Mei and Mai, but also Marie, who is heralded as a military legend despite being a retired soldier at the age of 19.
Colonel Kilgore: Gates.
Composite Character: Muse is essentially Sakuya, Alice, Remilia, and Patchouli rolled up into one character, except she predates all of them (except Alice.)
Crap Saccharine World: Although the world is slowly recovering from its environmental crisis, nearly all of the cast are involved with the military, either being Private Military Contractors or soldiers, which makes it clear that even The End of the World as We Know It hasn't eradicated wars. And then there are Mei and Mai, who are Child Soldiers at the age of five.
David Versus Goliath: VIVIT/Hirano goes up against stealth jets, Humongous Mecha, or dreadnought space battleships. The only time when there isn't a huge size difference is when you're fighting either Muse, Yuitia, Icarus, or the Touhou cameo characters, and they're all far stronger than any other opponents.
Deflector Shields: Serves as health in Kioh Gyoku. Getting hit by projectiles or enemies will lower the shield percentage; if it reaches 0, the shield will break, leaving your character vulnerable. If your character is hit while shields are down, they lose. Shields will slowly recharge as long as the character isn't hit, even if they're down. Also featured prominently on the player craft in Samidare.
Difficulty Spike: The first three enemies you face in Kioh Gyoku will probably kill themselves before you attack. Morgan puts up a bit of a fight. Muse, though...
Dirty Old Man: The omake all but outright states that VIVIT's design is relevant to Erich's interests.
Early-Bird Cameo/Older Than They Think: In the extra stage of the first game, Reimu and Marisa use their Windows designs. The game predates Embodiment of Scarlet Devil.
Fighting Your Friend: In stage 4 of Banshiryuu, you will fight against the character you didn't pick.
Fragile Speedster: Mei and Mai in Kioh Gyoku are very fast, but they arguably have the lowest defense in the game.
The Future
Genre Shift: Kioh Gyoku is a two-player versus shooter, much like the Touhou Phantasmagoria games.
Good-Looking Privates
Green Rocks: Saboten energy.
Have I Mentioned I Am Heterosexual Today?: One of Morgan's win quotes against Marie in Kioh Gyoku mentions that she's straight.
Hitbox Dissonance: Intentional, and highly encouraged, in the case of Kioh Gyoku.
Humongous Mecha / Powered Armor: Erich is fond of piloting these. They're known as the Hi-Beion line.
Improbable Age: Mei and Mai are 6 year old soldiers, Yuuta Kirishima can't be older than 15, and Marie is a retired legendary soldier at 18.
Fundamentally Female Cast: Averted, unlike its sibling series. Although the cast is still mostly female, male characters are featured in the games (and even playable, in the case of Kioh Gyoku.)
Lipstick Lesbian: Marie.
Macross Missile Massacre: One of VIVIT's shot-types in Shuusou Gyoku. Also a favorite tactic of Marie's.
Mission Control: Erich, for VIVIT. Gyoku, for Hirano.
Nintendo Hard
One-Winged Angel: The Final Boss of Shuusou Gyoku has three forms.
Power-Up Magnet
Power Gives You Wings : Marisa sports a pair of wings for her cameo appearance - She is more powerful here than pretty much any other appearance. The Final Boss of Shuusou Gyoku also has angel wings.
- Yuuka also gets wings for her cameo appearance, but she's probably weaker here than in any of her wingless appearances in her home series.
Recurring Boss: Gates and VIVIT (if you include all versions of her) are the only characters who are featured as an opponent in every Seihou game, including Samidare.
Science Fantasy: In a World of Science Fiction, there's Muse, a vampire alchemist who wants to combine magic and technology, and Yuitia, a ghost with tremendous power. Saboten energy also appears to have almost fantastical properties, if what happened to Erich's daughter Vivit is any indication. The protagonists are a shrine maiden and a robot girl, and the cameos feature a shrine maiden, a witch and a flower youkai.
Shotacon: Lagunas.
Shout-Out: Stage 4 of Banshiryuu is an extended Touhou Shout-Out based primarily on stage 4 of Lotus Land Story. It changes depending on who you're playing as like stage 4 of Lotus Land Story (and later Imperishable Night). If you're playing as VIVIT, you'll face the doofy ghosts that were common in the PC-98 games before facing off against a miko that throws aroung yin-yang orbs, like Reimu. Hirano goes through a stage quite similar to the original stage 4 of Lotus Land Story, before fighting VIVIT, who's already existing association with stars and lasers is ramped up, and she starts riding a broom just in case you missed that she's being Marisa.
Stalker with a Crush: Marie, towards VIVIT.
Stone Wall: Marie has very high defense in Kioh Gyoku and is the slowest character as well.
Super Move Portrait Attack: Boss attacks in Kioh Gyoku and the SE attacks used by bosses in Banshiryuu. Averted in the case of actual Bombs, with the exception of wide shot type VIVIT's bomb from Shuusou Gyoku, which does display a portrait.
Theme Naming: The title for each game is named after a cactus.
Tsundere: Hirano. Supposedly.
Updated Rerelease: The C74 version of Banshiryuu, which features a revamped layout, bullet patterns, new music, altered game mechanices, and the long-awaited Boss Rush Bonus Level of Hell. Your Mileage May Vary whether it is actually the better version gameplay-wise, as a lot of well-designed patterns were axed for unfair but flashy ones and vice-versa.
Whip It Good: Marie has a whip in Banshiryuu.
With Great Power Comes Great Insanity: (Human) Vivit and Yuitia.