Players take control of a gun-wielding demon hunter named Shou along with her house maid, the Gatling gun-toting Akari, as they fight off various monsters, undead creatures, and other supernatural forces when demonic forces break loose on one fateful night. The duo eventually run into a female grim reaper who overpowers Shou in battle and steals her soul, leading Shou and Akari to track her down to not only reclaim her soul, but find answers behind the outbreak and Shou's mysterious ability to steal souls of slain monsters. They are not the only ones hunting demons, as they also cross paths with the demon-hunting group known as the Undertakers.
Gameplay in Blood-over- is simple at a glance but far from a cakewalk; Shou has a simple Gun Fu attack with the Fire button and kicks with the Kick button, but certain directional combinations can be used to allow her to perform other attacks such a powerful explosive shot, a gun launcher attack, somersault kicks, and slides. Each successful attack you land on your enemies builds up Blood Points for your Blood Meter, which can be used for a devastating multi-gun shot attack at point blank range or call for Akari's assistance where she'll mow down her enemies with her Gatling gun. The crux of the gameplay, however, revolves around the Overkill System, which encourages players to dispatch enemies not just by simply killing them, but to overkill them and squeeze as much extra Blood Points as they're worth. This also ties into the game's dynamic difficulty system, which scales as the player earns higher scores. The game also features multiple endings; which one the player receives, however, is based on their performance.
Not to be confused with the 1996 Survival Horror game Over Blood.
This game features trope examples of:
- 2½D: The game uses 3D graphics with polygonal models for the characters, but the gameplay is solely 2D.
- Action Girl: Shou, who's a demon hunter capable of holding her own with her guns, kicks, and the ability to steal demon's souls. Akari is a maid with a Gatling gun who sits on the sidelines until she's needed.
- Attract Mode: If players wait for a moment before starting a game at the title screen, a demo of the first stage is played where Shou and Akari fight monsters in their mansion, up until after defeating the giant skeleton mini-boss.
- BFS: Nozomi carries one that oddly resembles Cloud's Buster Sword.
- Bottomless Magazines: Shou's guns, which she has a seemingly bottomless supply of ammo for them, as well as Akari with her Gatling gun.
- Combat Tentacles: Used by Sakuya when the demon takes over her and mutated her body. She'll use her tentacles to attack players from the ground or fire laser beams from their tips.
- Combos: Some attacks can be strung together in a sequence, allowing you to dish out as much damage as possible to enemies. The Overkill System works based how much Overkills you can carry throughout the game's stages.
- Combo Breaker: Taking damage will end your Overkill bonus instantly.
- Critical Annoyance: A single beeping noise will sound if the player's HP reaches 30 or below, with a "WARNING" shown next to Shou's Life Meter.
- Dem Bones: The skeleton enemies.
- Difficulty Levels: There are no selectable difficulty settings in the game, however, there are four difficulty levels that scales based on how well you play the game. From lowest to highest: Easy, Normal, Hard, and Nightmare.
- Doppelgänger Attack: Anri's fighting style revolves around using doppelgangers of herself to overwhelm her enemies.
- Dual Boss: Stage 3's boss consist of fighting a pair of devil twins, with the younger one fighting Shou up close and personal while the older one casts spells and sets traps for you from a distance.
- Dual Wielding: Anri fights by wielding two katanas in each hand.
- Dynamic Difficulty: The better you get at this game, the harder the game gets.
- Easy-Mode Mockery: Dropping down to Easy only gets you x0.8 of points the enemies are worth.
- Elevator Action Sequence: Halfway into Stage 5, where players fight monsters while taking an elevator to the top floor of monster-ridden skyscraper.
- Every 10,000 Points: Players can earn extra lives by scoring a certain amount of Overkill points. The first extend is at 20,000₧, then at 50,000₧, then finally every 100,000₧ thereafter.
- Faux Action Girl: Akari, who doesn't do much unless called by Shou. This even got lampshaded by one of the bosses of Stage 3 when they called her an "E-X-T-R-A".
- Final Boss Preview: The first stage ends with this.
- Gatling Good: Akari's weapon of choice.
- Gameplay Grading: The game grades you based on how much Overkill you were able to build on the stage and Total Overkill throughout the game, as well as any continues used.
- Guns Akimbo: Shou, who fights using two handguns.
- Hard Mode Perks: Getting the difficulty level up to Hard and Nightmare gives you a score bonus of x1.2 and x1.5, respectively.
- Hell Hound: A later enemy type is a demonic dog that can pounce on the player or breathe fire.
- Hopeless Boss Fight: Partway into fighting the grim reaper lady in the first stage, she ends the fight by stealing away Shou's soul and the stage ends from there.
- I Never Told You My Name: The mysterious grim reaper lady that Shou and Akari run into in the first stage never told them her name. If players manage to get to the true ending path, the grim reaper tells them her name is Sia.
- Invulnerable Attack: When players call Akari (or Akari saves the player when their Blood Meter is maxed), they're given a brief moment of invincibility while Akari mows the lawn of her enemies.
- Kick Chick: Shou's other method of attack is kicking enemies, a lounging rolling sobat to close gaps, or a somersault kick that can send enemies upwards.
- Launcher Move: Down+Attack will cause Shou to perform an upwards power shot that will send most enemies flying, which she can follow up with another attack. She also has a somersault kick that can be performed by inputting a Quarter-Circle Forward+Attack, which can hit multiple enemies but doesn't give much room for follow-up attacks.
- Life Meter: The Life Meter, which Shou only has 100 HP. The meter is colored blue for 70 points of her life in segments, while the last 30 is colored red.
- Limit Break: This how you call Akari to gun down enemies with her Gatling gun. Shou has one of her own where she unloads super-powered bullets onto her enemies.
- Mana Meter: The Blood Meter, represented by the Moon which is built up not just by fighting enemies, but also fills up faster by Overkilling them. It maxes at 300 Blood Points, with the Moon turning red.
- Multiple Endings: If you can score high enough and beat The Very Definitely Final Level.
- Night of the Living Mooks: Skeletons, hell hounds, and demons are just the norm for this game.
- Ninja Maid: Akari, who may look your typical house maid, but she's quite skilled with a Gatling gun to protect Shou.
- One-Hit Kill: The boss in Stage 2, if he grabs you when turning red. His attack deals 9999 damage yet you only have 100 HP!
- Rank Inflation: The game grades you based on your performance across each stage and overall score, between a rank of D- to S.
- Red Eyes, Take Warning: Sayuka, Shou's younger sister, has red eyes after devouring many demons.
- Scoring Points: You gain points based on the damage you deal to enemies, but there also extra points that can be milked out of enemies by Overkilling them, which starts a combo meter that gradually diminishes until you find another enemy to fight or drops instantly from take damage from their attacks. The amount of Overkill you can get also varies between each enemy type. The difficulty the player is in also affects how the score multiplier; Easy only nets you x0.8, Normal gives x1.0, Hard gives x1.2, and Nightmare gives x1.5. Mastering this system however is key towards getting extra lives and reaching the game's true ending.
- Superpowered Evil Side: Shou enters an Overdosed state during her encounter with Anri, causing her inner demonic powers to kick in and give her a x1.5 Attack Boost during the fight. Unlike her sister, however, Shou manages to fight it off before it took over her after defeating Anri.
- There Is No Kill Like Overkill: The game's scoring system is built around trying to squeeze as much Blood Points out of your enemies by overkilling them, taking down their blue health meter and pumping as much red overkill damage as possible.
- Title Scream: One of the characters in the game will say the game's name upon seeing the title screen.
- True Final Boss: Shou's sister, Sayuka, although Shou's trying to save her from the demon that's taken over her.
- Turns Red: Many bosses you encounter gains more difficult and dangerous attacks as they get closer to defeat.
- Video-Game Lives: The game features lives, which players only start out with 3 per credit. To get more lives, players much get acquainted with the game's scoring system and earn them via extends.
- World of Action Girls: 92% of the game's cast are Action Girls whom are capable of kicking ass one way or another, while The One Guy happens to be a towering demon guy as Stage 2's boss.
