Quantum Theory

Quantum Theory (クウォンタム セオリー) is a sci-fi third-person shooter that merges platforming elements with the use of a cover system.

Keisuke Kikuchi was the game's executive producer while Makoto Shibata handled its direction.

The limited edition box includes an original soundtrack, a special concept art book, and a serial code containing the Shiranui and Murakumo mercenary skins for online matches. Those who reserved early copies receive a code featuring a unique weapon and a special multiplayer Valkyrie skin.

Plot
Set in a post-apocalyptic era, a hazardous phenomenon known as the Erosion has brought humanity to its knees. It takes the form of an impregnable tower that attracts beings known as Diablosis. Any organism that comes into contact with Diablosis becomes infected and hostile, leading to numerous deaths and environmental disasters.

With the Tower's presence causing the Diablosis to spread out of control, the protagonist Syd aims to destroy it to mitigate the damage. Ascending to the top alongside a mysterious woman named Filena, the two of them learn some disturbing truths about the Erosion and its purpose.

Gameplay
To attack an enemy, hold L1 to aim at them and press R1 to fire. The reticle will turn red if it toggles unto a hostile target. When running out of ammo, the player can manually reload their weapon with R2; though shooting is not possible while reloading, other actions like evading can still be done. Firing at an enemy's weak spot will inflict more damage than usual and may even kill them instantly.

The left analog stick is used to move from one spot to another; holding enables the player to run at a faster pace. Launching a melee attack while running will trigger a dash hit. Although the timing is tricky, it can be useful in knocking down weaker foes or conserving ammo.

Some areas contain movable terrain that must be traversed by tapping at the right moment. Failure to act at the right time will result in death, causing the player to return to their last check point. Moving layouts make aiming more complicated, so it is recommended to prioritize more on nearby targets.

Upon receiving damage from enemy attacks, the screen will turn red to indicate injured status. The screen returns to normal after a few seconds of not being attacked. If the player sustains too many injuries without resting, they will simply die.

Two methods of avoiding damage are performing evasive rolls and hiding behind covers. is used to evade approaching foes. While useful in open battlefields, care should be taken not to do it near ledges. allows the player to take cover behind nearby objects and give themselves time to recover while counterattacking from a safe spot. However, some covers will break after being shot at enough times, forcing players to find protection elsewhere.

Difficulty levels consist of Easy, Normal, and Hard.

Multiplayer options include two different challenges: Team Battle and Battle Royale. Matches take place in a variety of layouts from the main mode while participants can choose between several character skins and weapons.

Characters

 * Syd
 * Filena
 * Nyx - Voiced by Megan Hollingshead. Syd's former partner and a Gillskin who fights like Filena, Nyx is a feisty and rash individual. Though she was able to help Syd destroy an infected Tower, its destruction meant her body would die out. Syd is forced to leave her behind as the Tower collapses. She can be unlocked in multiplayer matches by attaining the trophy "Death & Rebirth".
 * Franz Croft - Voiced by Keith Szarabajka. Franz is the leader of a small militia tasked with invading the Tower that sprouted in their colony. He initially interrogates Syd, but ends up relying on his aid when the Diablosis attacks them. Upon entering the Tower's main hall, he dies fighting the Nosferatu stationed there. Syd leaves a coin next to Franz's corpse as a sign of respect for his valor. He is playable in multiplayer matches.
 * Jim Morrigan - Voiced by Patrick Seitz. A member of Franz's militia group. Jim is constantly on edge out of worry for his wife and child. He is the only other squad member to make it inside the Tower, though is unceremoniously killed off by the Nosferatu. He is playable in multiplayer matches.
 * Lainie Lorenz - Voiced by Laura Bailey. A member of Franz's militia group, Lainie is killed together with Shiro while trying to ascend to the Tower's entrance. She is playable in multiplayer matches.
 * Shiro - Voiced by Troy Baker. Affiliated with Franz's militia group, Shiro distrusts Syd during their investigation of him. He dies trying to evade the Tower's defense system. He can be unlocked in multiplayer matches by attaining the novice rank.
 * Fear - Voiced by Steven Blum. Syd's old mentor. An experienced veteran with a devil-may-care attitude, he led a group of Gillskin exiles to destroy underground Nosferatu before being killed during the Seed's germination. His weapon and combat philosophy were inherited by Syd for years to come.
 * Xex - Voiced by Keith Szarabajka. A member of Syd's former Gillskin group, he and Fear have something of a rivalry despite being in the same faction. He can be unlocked in multiplayer matches by attaining the mercenary rank.
 * Elev - Voiced by Laura Bailey. A member of Syd's former Gillskin group. Entrusted with the task of destroying the Seed before it can germinate, Elev ends up being impaled by its tentacles before activating the detonator she implanted on it. She can be unlocked in multiplayer matches by attaining the trophy "Fetus".
 * Zolf - Voiced by Troy Baker. A member of Syd's former Gillskin group, he is the first among them to be killed by a Stillborn.
 * Thanatos - An extraordinary Gillskin with a god complex to match, Thanatos aims to become the strongest creature in existence by infecting the whole Tower with Diablosis. He seeks to make use of the lumenosynthetic reactors and later Filena to fulfill his twisted vision of the world. During his confrontations with Syd, Thanatos tries to appeal to the latter's baser instincts by goading him into fighting.
 * Xeust Lambert - A researcher whose journal entries are displayed before the start of each scene. Implied to have been the creator of the Seeds and by extension the Nosferatu, his primary goal was to save the world by introducing perfected life forms to sustain it. He believed that humanity would stop bickering among themselves if they had a common enemy to fight against.
 * Seed - Voiced by Steven Blum, Patrick Seitz, and Lani Minella. Enigmatic beings that result in the creation of Towers. They are spread throughout the world and share data via wireless network to perfect their humanoid experiments.


 * Glossary
 * Tower
 * Erosion - An catastrophic phenomenon that results in the mutation of living organisms and environments. It is a by-product of the Lost Age and much of it has ruined surviving human settlements.
 * Gillskin - Living organisms infected or created by the process of Diablosis. Artificially-enhanced humans are considered Gillskins, though they do not display any physical mutations other than glowing red pupils and more muscle mass. Many are generally hostile to the Nosferatu. Some Gillskins have flammable properties or regenerative qualities, the latter trait being most prominent in beings like Syd.
 * Nosferatu - Humanoids created by Seeds, these beings are tasked with guarding the Tower from intruders, basically acting like white blood cells for the structure itself. Most Nosferatu lack free will and agency in their actions compared to Gillskins who act more in instinct. They typically sport more elaborate appearances to match the Tower's interior design. Nosferatu may also turn into Gillskins via Diablosis.

Navigation

 * Enemies & Obstacles
 * Legend

Related Media
The game was first introduced in a press conference at TGS 2008.

A promotion video was shown on March 25, 2010.

Both the executive producer and director held a gameplay demo at a Yamada Denki store in Ikebukuro.