Maxwell's DemonWP (マックスウェルの悪魔, Makkusuweru no Akuma?), Class Name Caster (キャスター, Kyasutā?), is the Caster-class Servant of the Fuhrer in the Imperial Capital Holy Grail Strange Story of Fate/KOHA-ACE, and the Servant of an unnamed Master in its remake Fate/type Redline. He is the Servant of High Priest Makuzu in Fate/Grand Order.
Maxwell's Demon is a fictional demon created by James Clerk MaxwellWP as a thought experiment, distorted by the desires of people.
Caster has short, well groomed orange hair, and is dressed in a tan business suit with a red tie and sunglasses. While his general appearance is unchanged in his appearance in Fate/Grand Order, his colour palette has shifted drastically to light brown hair, a two toned green suit and black tie.
Maxwell's Demon appears in Fate/KOHA-ACE. The events of the Imperial Capital Holy Grail Strange Story would be later re-adapted in a more serious tone in Fate/type Redline.
GUDAGUDA Final Honnōji
Caster came to check on Okada Izou after his conversation his Master. Assassin thought Caster came to get his report from him, he reminds Caster about his Master's report on him, he did get the report. When Assassin thinks he refers to the magus he fought, but he wasn't talking about her, he is talking about Saber's Master. After Assassin informs him what he knows from the other day and asks why he's interested in him, he smiles and asks Assassin he would appreciate it if he could tell him more about him.
Maxwell's Demon is a conceptual Servant. He is merely a Demon formed by a thought experiment of a scientist, and a servant distorted by the desires of people. A theoretical concept. Although Okita Souji is able to easily cut through him, it doesn't hinder him at all. He claims that no servant that can defeat him exists in modern era. Simply put, one who can resolve the theory of his concept does not exist. Maxwell's demon says he doesn't negate the idea of someone from the distant future being able to resolve him.
By using this Noble Phantasm, along with the Holy Grail, Caster is able to use the Right Hand of Glory and the Fuhrer corrupted by the Holy Grail Mud as a Catalyst to summon the "True Fuhrer", Neo Fuhrer. Even the combined efforts of Okita Souji, Oda Nobunaga empowered by all Command Spells, and spearless Li Shuwen are unable to take it down. It took summoning Okita Souji Alter as a Guardian of the Counter Force to defeat him with her Absolute Sword - Endless Three-Stage.
 Fate/KOHA-ACE - STATUS: Caster, p.157
Master: Mysterious Person
True Name: Maxwell
Alignment: True Neutral
Noble Phantasm: -
■ Devil’s Proof: EX
■ Maxwell's Demon: Negation of the Second Law of Thermodynamics
Type: Conceptual Noble Phantasm
Maximum Targets: -
The infinite heart that greedy humanity dreamt of. It is a perpetual motion machine manifested by the denial of the second law of thermodynamics. However, it is not a perfect perpetual motion machine but merely something resembling it.
It has an effect that allows it to produce close to an infinite amount of energy; however, there are several conditions to its invocation.
- Fate/KOHA-ACE - Chapter 1
- Fate/KOHA-ACE - Chapter 2
- Fate/KOHA-ACE - Chapter 3
- Fate/KOHA-ACE - Chapter 4
- Fate/KOHA-ACE - Chapter 5
- Fate/KOHA-ACE - Chapter 6
- Fate/KOHA-ACE - Chapter 7
- Fate/KOHA-ACE - Chapter 8
- Fate/KOHA-ACE - Chapter 9
- Fate/KOHA-ACE - Chapter 10
- Fate/KOHA-ACE - Chapter 11
- Fate/KOHA-ACE - Chapter 12
- Fate/KOHA-ACE - Chapter 13
- Fate/KOHA-ACE - Chapter 14
- Fate/KOHA-ACE - Chapter 15
- Fate/type Redline - Chapter 9.2