Melty Blood: Act Cadenza is a horror-fantasy 2D fighting game developed by Ecole (along with Soft Circle French-Bread and Type-Moon) and released by Sega for arcades (using Dreamcast-based Sega NAOMI hardware) exclusively in Japan on March 25, 2005.
Along with an updated "Ver. A" revision on August 5, 2005, which made numerous balance updates, the game received a console port for the PlayStation 2 on August 10, 2006. Released exclusively in Japan by Ecole, the PS2 version includes further balance tweaks (which can be disabled for the authentic arcade experience) and new unlockables.
The PS2 port was later used as the base for the arcade version's updated "Ver. B" revision on December 23, 2006. This version also adds a fifth button as a shortcut for certain commands and made the boss character White Len playable. This version was later ported to the PC on July 27, 2007. The PC version, also released by Ecole, adds further changes while including new features (such as tag-team).
Much of the gameplay from Melty Blood (as of its Re-ACT expansion) remain intact. However, there are a few differences:
- Certain techniques now make use of multi-button command inputs, such as throws (which are now performed by pressing A+D with a direction) and Heat mode activation (which is now performed by pressing A+B+C). Players can also perform dashes by pressing A+B with a direction.
- Rather than a frames-per-second counter, the game includes a traditional round timer.
- Players can now use the Heat mode activation command while in hitstun or blockstun on the ground to perform a Circuit Spark. Similar to Psych Bursts in the Guilty Gear series, Circuit Sparks cause the character to cancel out of their stun into a low-damage knockback attack. Regardless of whether players use this instead of Heat or Blood Heat, it fully depletes the Magic Circuit gauge.
- Certain attacks (namely most Last Arcs) cause a Circuit Break against an opponent, temporarily halting the accumulation of their Magic Circuit gauge.
- Shield Counters have been removed.
All characters/variations, with the exception of the G-Akiha and "fully-armed" Ciel variants, return from Melty Blood (and its Re-ACT expansion). All characters, with the exception of White Len and Neco-Arc, are playable from the start. The game includes 21 playable character slots (23 as of the PS2 version and 24 as of the Ver. B and PC versions).
Unlike other games in the series, Act Cadenza has the romanization of Japanese names reversed.
- Kouma Kishima - Originally appearing in the visual novel Kagetsu Tohya, Kouma is a reclusive hermit from the past with a bloodline that is more demon than human (and was originally responsible for eliminating the rest of Shiki's bloodline). He is a nightmare form created by "Tatari" and is a skilled martial artist.
- Sion Eltnam Atlasia - An alchemist from the Atlas Academy who was turned partially into a vampire from the mysterious "Tatari", and must travel to Misaki Town to find a cure. Along with superhuman analytical powers, she uses a wire "ethelite" whip and a handgun in combat. She has a fully-vampiric nightmare form (Sion TATARI, or Kyuuketsuki Sion) as an alternate character.
- Shiki Tohno - A high-school student who was born with eyes that allow him to see "lines vulnerable to death" on a person's body, letting him kill almost anyone with a simple knife as long as he cuts along those lines. He is an adopted son of the Tohno family, originally part of the Nanaya family of demon hunters. He has a murderous nightmare form (Shiki Nanaya) as an alternate character.
- Arcueid Brunestud - A genuine vampire and a "True Ancestor" who has lived for over 800 years through constant hibernation, only to become close with Shiki after he "killed" her. She also has an alternate "berserk" version (Red Arcueid, or Bousou Arcueid) as an alternate character.
- Ciel - An upperclassman of Shiki at his high school, but happens to be a skilled exorcist and member of the Holy Church's "Burial Agency". Along with martial arts, she carries a variety of blades (known as the Black Keys).
- Akiha Tohno - The head of the Tohno family and Shiki's adopted younger sister. She also has supernatural powers due to having a part-demonic bloodline. She has a more-demonic nightmare form (Akiha Vermillion, or Sekishu Akiha) as as an alternate character.
- Hisui & Kohaku - The twin maids of the Tohno estate, with Hisui as the quiet introvert and Kohaku as the cheerful extrovert. As comical relief characters, both fight with a variety of cleaning objects. While they can be played as separate characters, they can also fight as a unique "tag-team" character in which players can switch between Hisui and Kohaku, using a dedicated special command, and have unique team attacks.
- Nrvnqsr Chaos (Nero Chaos) - A chaotic vampire and one of the Dead Apostle Ancestors, with 666 beasts contained in him.
- Warachia (Warakia no Yoru) - A mysterious vampire, one of the Dead Apostle Ancestors, and is the manifestation of an entity known as "Tatari".
- Mech-Hisui (Mecha-Hisui) - A robotic clone of Hisui created by Kohaku for a mysterious purpose. Due to the effects of "Tatari", her A.I. often malfunctions (causing comic relief).
- Miyako Arima - The eldest daughter of the Arima family, who Shiki has lived with for years. She is very proficient at the martial art of bajiquan despite her young age.
- Len - A familiar with the ability to manipulate dreams. She can transform between a cat and a young human girl. Has a mysterious doppelganger White Len (or Shiro Len) as a boss character, who is only playable in the Ver. B and PC versions.
- Satsuki Yumizuka - A classmate and childhood friend of Shiki, Satsuki was killed in a serial murder, only to be revived as a vampire (who tries her best to carry on being an ordinary human).
- Aoko Aozaki - One of the few remaining sorceresses in the world, Aoko is an older friend of Shiki who helps him control his powers (while having various magical abilities of her own). This is the first game where she is playable.
- Neco-Arc - A joke character and a cat-like super-deformation of Arcueid. Boss character who was made playable as a hidden unlockable in the PS2 version. In the PS2 version, players can also unlock five alternate voice sets for her to use, along with an alternate Neco-Arc Chaos version (with the voice, likeness, and abilities of Nrvnqsr Chaos). Both regular and Chaos version were made playable from the start in the Ver. B and PC versions, with the PC version adding two unplayable boss variants: Damien Armies (four Neco-Arc Chaos clones fought sequentially) and Neco Chaos Black G666 (a giant robotic version of Neco-Arc Chaos created by Kohaku).