The first game in the series, Koumajou Densetsu: Scarlet Symphony, features Reimu Hakurei from the Touhou Project as its main character. The story: Gensokyo is covered in a scarlet mist... Again. Reimu Hakurei sets out to the Scarlet Devil Mansion, since that was where the previous scarlet mist incident happened previously, to fix this problem. Along the way, she meets Marisa Kirisame, who joins Reimu, and Cirno, who attacks Reimu at first, but eventually ends up joining Reimu's party. Together they fight through the newly built Scarlet Devil Castle, guarded not only by fairies and the other usual inhabitants of the Scarlet Mansion, but also by enemies straight taken from the world of Castlevania like the Medusa Heads, until they finally reach the mistress of the castle and discover the shocking truth...
For foreign players, Frontier Aja included in the v1.03 patch an English and French translation for the Story Mode.
In 2010 it was succeeded by Koumajou Densetsu II: Stranger's Requiem, which features voice acting by professional seiyuus, and Sakuya Izayoi, Remilia's head maid, as the main character. In this story, Sakuya has just returned to the Scarlet Devil Mansion only to find its inhabitants missing. Border youkai and overall troll Yukari Yakumo then appears before Sakuya and informs her that spring is late to arrive... Again! Sakuya travels to Hakugyokurou to investigate, where she discovers a rebuilt Scarlet Devil Castle built around the youkai cherry tree, the Saigyou Ayakashi.
The second game builds around many of the concepts of the first, and adds more sub-weapons in the form of partners, most of whom replicate the sub-weapons found in Castlevania (for instance, Meiling launches herself at an upward angle, then comes back down not unlike the axe, and Reimu throws a yin-yang orb that travels like the cross). The gameplay is also more polished, with fewer cheap shots and better balance overall.
In 2011 during Winter Comiket 81, Frontier Aja released the Koumajou Densetsu Premium Pack, a fully updated re-release of Scarlet Symphony and Stranger's Requiemnote with an abridged version of the soundtracks, character artworks, and sprites of the characters and enemies from both games in one package.
On June 5th, 2021, it was announced that the first game in the series would be coming to the Nintendo Switch and Steam for the first time as Koumajou Remilia: Scarlet Symphony. This release features a few new additions, including a Super Easy mode, a Suika assist, and most notably, full voice acting. It released on July 29, 2022. On September 12, 2022, the game's sequel was announced that it too will also be re-released onto the Nintendo Switch and Steam in the near future.
Alongside those the from Touhou Project and the original Castlevania games, the tropes in these games are:
- Anime Theme Song: The opening theme afraid from Stranger's Requiem.
- Annoying Arrows: Averted; Those arrows will hurt. Especially if loosed by those Goddamned Red Archer Fairies.
- Art-Style Dissonance: An inversion of the normal use. The visuals are the only thing that's really any darker than the original Touhou games.
- Awesome, but Impractical:
- Sakuya's Stopwatch is useful in only a handful of situations.
- Flandre, after Stage 6 and Remilia, in Phantasm, as partners; the two are your heaviest hitters, the former dealing good damage in a wide circular area, the latter doing crazy damage in a spear shaped area. The disadvantage? They cost a lot of souls in order to summon them, when you can simply use a combination of your skills and partners like Meiling and Alice plus Sakuya's Knives to handle pretty much anything in the game. Doesn't detract from the "Holy Shit!" factor the first time you summon them, though.
- Ax-Crazy: Flandre really went off the slope in the second game.
- Badass Cape: Marisa in the second game.
- Berserk Button: Sakuya does NOT take kindly to anyone messing with her mistress.
- BFS: Flandre's Laevateinn doesn't look so intimidating at first glance at her sprite, right? Then she starts swinging around the gigantic laser blade. Also, Remilia's Gungnir is quite the Blade on a Stick. Apart from getting a design overhaul, it is larger (and rather heavy looking) than Remilia is on top of spawning lasers from its flight path. Try getting hit by the attacks where those weapons are involved. Go ahead and see how much damage a direct hit will inflict. Hint: You may lose as little as 40% (laser) to up to 80% (direct hit).
- "Blind Idiot" Translation: The first game was translated into English and French by Frontier Aja themselves. While the translation is for the most part readable and isn't anywhere close to the level of, say, Zero Wing, it does have a few instances of this.
- Surprisingly Good English: The second game mostly averts this, however, as the translation of that game is pretty good.
- Bonus Boss: Flandre in the first game, and Yukari in the second. However, while the second game's Brutal Bonus Level is longer and harder than the first game's, Flandre is harder to defeat than Yukari.
- Brainwashed and Crazy: A possibility for why Remilia went along with Yukari's plan, another being Grand Theft Me.
- Brutal Bonus Level: Both of the Extra Stages in general, but especially the second game's Phantasm stage, which introduces a host of new and annoying enemies. It's also quite long to boot.
- Calling Your Attacks: Marisa does this in the second game with her Master Spark.
- Crossover: Between Touhou Project and Castlevania
- Darker and Edgier: The designs and settings look very grown up and dark. But the story and characterizations are every bit as nutty as its mainstream counterpart.
- The second game plays it pretty much straight, seeing as how Yukari has brainwashed Remilia and is gathering fighting power into the Saigyou Ayakashi (and Remilia) to make a full bloom. Do note that it's already been established in Touhou canon that the Saigyou Ayakashi is the one truly evil thing in all of Gensokyo and a full bloom would be very bad. Flandre also goes to her fanon portrayals of being a genocidal, amoral maniac.
- Defeat Equals Friendship: Cirno in the first game. Alice, Reimu, and in the Phantasm Stage, Remilia in the second game.
- Subverted in the second game with Marisa. Sakuya tries to get her to help them after their battle, but she refuses and goes off to find something to pilfer in the castle. Instead, you get Alice, who WAS defeated earlier in the game.
- Elegant Gothic Lolita: Everyone's clothing takes a turn towards this.
- Elite Mook: In the Extra and Phantasm stages. These are enemies with a palette swap. They not only attack a lot faster than the regular versions and take more punishment before going down, they do more damage and some of them gain new forms of attack altogether. The one enemy guaranteed to make you rage will be the new Elite Archer Fairies.
- Evil Laugh: Several bosses in the sequel. Surprisingly, Reimu has the most impressive one!!
- Energy Weapon: And how! Many a Castlevania veteran would have a heart attack dealing with Bullet Hell in their Metroidvania as it is, but some of these bosses can throw enough stuff at you to start throwing you around as you take damage. Then you get to Marisa in the second game and have to deal with her laser barrage. And any encounter with Remilia cannot go on without her throwing Gungnir at you and you scrambling to get out of her insane range thanks to laser beams spawning at revolving angles from the spear's trajectory.
- Thought the above girls were bad enough? Once you finally struggle through the Phantasm stage and reach Bonus Boss Yukari, her opening move will not only put the above girls to shame, it will also likely elicit the appropriate reaction from you. And she's barely getting started.
- Extra Lives, 1-Up: Shaped like Yukkuris! There's always one well hidden in each stage, but beware of the Schmuck Bait mentioned below!
- Expy: Expected, since these games are Castlevania with Touhou characters in place of the usual ones. These are just some examples):
- Reimu: Of the Belmonts, but especially of Trevor and Richter.
- Remilia: Obviously, of Dracula. The second game adds on the Symphony of the Night shout-outs and also adding some of Dracula's moves to her attack pattern. Subverted in the sense that she never meant to do any real harm to anyone. At least, out of her own will...
- Sakuya: In the first game, of Death. In the second game, of Alucard. Then subverted again; Sakuya, unlike Alucard to his father, is unquestionably loyal to Remilia. There's also her already-present expy to Dio Brando.
- Patchouli: Of Sypha Belnaldes.
- Komachi: Of The Ferryman.
- Yuyuko: Of Death, in the second game. Another Subversion; she holds no loyalty to Remilia, and in fact may have been working to control her along with Yukari.
- Saigyou Ayakashi: POSSIBLY of Chaos, given how it uses Remilia and makes her go One-Winged Angel, while in the original Castlevania series, Chaos is the source of Dracula's power. They're also both very much Eldritch Abominations, so there's that.
- Face–Heel Turn: In the second game, Reimu is asked by Yukari to watch over the newly built castle in Hakugyokurou. Not that there's anything wrong with it, because it looks very awesome.
- Fake Difficulty: A criticism of the first game. There simply isn't enough room on the screen to display everything. As a result, it is not uncommon to walk right into a bird that suddenly appears out of nowhere in the very first area! Annoyingly, the action zooms out for boss fights. There is also the unfair "critical hits" that you take from enemies and bosses that you can't do to them. This is thankfully remedied in the second game.
- Though, not completely. Critical hits can still happen in the second game, but much less frequently. Still, getting blown down to near-death from full life after eating a Gungnir to the face is particularly cringe-worthy.
- Fastball Special: Ran, as usual, will throw Chen into the fight at regular intervals. Yukari throws Ran and Chen out as well.
- For Doom the Bell Tolls: Flandre's theme in the first game has this. Considering who you're dealing with, it's hardly surprising.
- Glowing Eyes of Doom: Remilia displays these when she goes One-Winged Angel.
- Grand Theft Me: A possibility for why Remilia went along with Yukari's plan, this time the reasoning being that the Saigyou Ayakashi possessed the former before the final battle. Given that the Saigyou Ayakashi is closely related to another certain character with the power to invoke death, this also explains the whole "acquiring the power to manipulate death whilst alive" thing.
- Gratuitous English: The chorus of the second game's Final Boss theme, "Rose-Killing Carmilla".
- Hellish Pupils: Flandre and Remilia, though it's much more noticable in the former's eyes.
- Hitbox Dissonance: Your hit-box is a lot smaller when flying. However, because you do much more damage with your regular attack on the ground, it's really only recommended that you use this to avoid enemy attacks rather than offensively.
- Insane Troll Logic: What was Remilia's motivation for creating the Scarlet Devil Castle and releasing the Red Mist again? Because she read a magazine about buried treasure near the "Red Castle" and wanted to dig for it, so she had Sakuya build the Scarlet Devil Castle and expected buried treasure to magically appear but she needed to work both day and night. Marisa calls her out for being an even bigger airhead than Cirno on that one.
- It Amused Me: Basically summarizes Yukari's actions; however, it seems to border on For the Evulz at times.
- Kaizo Trap: Yukari's special attack in the Phantasm stage of the second game. Even if you manage to kill her before she can disappear, it will continue to go on until you grab the crystal (and is more than capable of killing you in that time).
- Karma Houdini: Yukari in the second game. Made even more annoying by the fact that while you do get a boss fight with her, it's more of a Warm-Up Boss in preparation for Remilia's final form, as her attacks are simple and she doesn't even use a special attack like all of the other bosses. She's just toying with you.
- She doesn't even get her comeuppance in the Phantasm stage as the "plot" is completely unrelated to her actions in the main game and instead focus on her having invited the other girls for a Danmaku festival.
- Large Ham: Ran surely likes to put the hog derivatives in her lines in the second game. It's quite noticeable compared to the rest of the cast.
- Life Drain: Remilia gets props for being the sole Touhou boss to pull this on you yet, but will only do so in the second game; Getting hit by this thing results in losing a good third of your Life Meter, accompanied by a discouraging life meter recovery for Remilia. On Normal and below, dodging it is easy. On Hard, though...
- Mind-Control Eyes: Remilia sports these when possessed by Saigyou Ayakashi and forced to go One-Winged Angel.
- Mood Whiplash: The second game is very serious, but the Phantasm stage is about fireworks.
- Also in the first game where Remilia hid away after finding an ancient book, ordered Sakuya to build a red castle and lured Reimu and Marisa to come, all so that she could have a treasure hunt... When she reveals this, the music stops playing and is replaced with bird tweets. After the situation is cleared up (in a sense) it ends with Cirno calling Remilia an idiot.
- The confrontation in II after the Reimu fight seems to be heading for a dramatic confession from Reimu about her motives, only to veer into a declaration from Reimu that she quits.
- Navel-Deep Neckline: Yukari has a neckline that exposes all of her cleavage and a part of her stomach.
- Nightmare Fuel Station Attendant: Flandre in the second game.
- Nintendo Hard: It's the lovechild of Touhou and Castlevania. What did you expect?
- The second game isn't that hard, however. Other than the Phantasm stage.
- No "Arc" in "Archery": Subverted with the bow faeries in the second game, who are shockingly accurate with their arrows.
- Noblewoman's Laugh: Reimu, of all people, sometimes does this when performing her special attack.
- No Fair Cheating: Reimu can fly indefinitely in the first game. Think you can use this to bypass many of the hazards in the wide open stages? Wrong. The top of these areas are often full of red puffballs that will chase you relentlessly if you get anywhere close to them. The second game alleviates this problem by limiting the amount of time Sakuya can fly.
- Omake: After you complete the second game, an item called "Omake" is unlocked. This consists of four skits featuring the characters in the game in a bit of comedic slice-of-life.
- In the game's Compilation Rerelease, it includes the abridged soundtracks, illustrations, and sprites from both games.
- Ominous Pipe Organ: Remilia's theme in the first game has these together with a bit of For Doom the Bell Tolls.
- One-Winged Angel: Surprisingly averted in the first game. This being a Castlevania clone and Remi being Dracula's expy, some would expect her to turn into some ugly and absurdly powerful monster after beating her once. Instead, the second half of the final battle is a Boss Rush. The second game plays it straight, though. After beating Remilia and Yukari, she turns into some kind of giant monster cage with her inside, not unlike Dracula's throne in Symphony of the Night.
- Red Eyes, Take Warning: Subverted with the Scarlet sisters, since it's their natural eye color.
- Played straight with Sakuya just before the final battle where her eyes start to glow red.
- Schmuck Bait: In the second game, you can get a 1up at the final stairway before Remilia by standing on the awning above the stage entrance. The 1up falls on top of you. You come across this same area again in the Phantasm Stage, but if you try the trick here, a huge doll head falls on top of you instead, resulting in a One-Hit Kill if it hits you. If you manage to dodge the doll head, however, an actual 1up will appear.
- She Is Not My Girlfriend: Marisa and Alice in the first game. Hilariously, in the second game, the whole reason Alice came to Scarlet Devil Castle is because she was worried about Marisa. And when Marisa leaves Alice behind as she leaves, the Scarlet Mansion residents express sympathy for Alice having been dumped.
- Shout-Out: Apart from the expected shout-outs to Castlevania, there's also one that any Touhou fans well-acquainted with the series' memes should have been expecting upon learning that you can use Sakuya's Stopwatch in the second game:Sakuya: *Uses Stopwatch* "Watashi no sekai..." ("My world...")
- The omake with Remilia and Sakuya ends with Remilia declaring Sakuya the winner of a contest to see who could alleviate her boredom the best, and upon the others expressing their disbelief, she launches into an adorable "Urusai, urusai, urusai!"
- This Is Unforgivable!: In the second game, by the time that Sakuya confronts Yukari during the final battle, she's plenty pissed off for what Yukari put her ojou-sama through, and she lets her know this in no uncertain terms.Yukari: "Ah, I wonder if the air was too heavy for a vampire."
Sakuya: "Yakumo Yukari... you!"*
Yukari: "Hahaha... don't let yourself boil over yet. There's more to come."
Sakuya: "I can't... I'll never forgive you for this!"*
- Throwing Down the Gauntlet: Remilia in 2 does this in pure "What is a Man?" fashion.
- Time Stands Still: As in the games these games are based on, this is Sakuya's main power. Time can be stopped for up to three seconds before resuming, though certain enemies are immune to the ability.
- Took a Level in Badass: You got it. No member of the cast has lost a bit of the sheer awesomeness they had in the original games, and in fact, they have gained some levels in badass looks. Yes, even Cirno and Chen. Made all the more apparent in both games' extra stages, where everything Takes a Level in Badass.
- Unexpected Character: The three fairies of light in the second game's Phantasm stage. No art for them however.