A consultant magus from the Imperial Army, 24 years old. He comes from a family of magi who communicate with spirits. Due to the Holy Grail War, he was especially invited into the Army in 1943. Two years ago, he took in Kaname after she was cast out, giving her his protection, and making her serve under him in the army. He was a lieutenant of the 2nd Magecraft Division and created the Heroic Spirit Summoning Mechanism No-Riku unit. Using the summoning system, with Kaname being utilized as a mana tank, the Army used it to summon Oda Nobunaga but they were incredulous when the one known as the Demon Lord turned out to be a woman. After Archer decapitated her initial Master for looking down on her, Magatsu and every man in the facility prostrated to her as if begging for forgiveness. Now that Archer was Masterless, he thinks to himself that he's the obvious choice to be her new Master but was devastated when she asked Kaname.
A few weeks before the Holy Grail War of 1945 began, Magatsu receives Major Reiter and a Colonel from the German Third Reich form a new alliance between Imperial Japan and the Third Reich for the Holy Grail War. Shown a presentation of the Berserker Class with an overhead projector, he is asked by Reiter to summon a Berserker and that they are willing to lend him the IV-Type Heroic Spirit Restraining Device (IV型英霊拘束具?) so that he can control its power. Magatsu agrees and promises to provide them with an hiding place within the imperial capital, but he asks why they are willing to give it to him, to which the Colonel replies that those with power will gain more power.
Magatsu appears superficially similar to the character he is replacing, having mid-length wavy hair akin to Shinji Matou, but being taller and more serious looking with rectangular spectacles and a Imperial Japanese military uniform.
Magatsu is something of a cold and manipulative individual, referring to Archer merely as a 'thing' rather than as a person and seems to regard the true nature of Oda Nobunaga as a sort of cruel joke. He shows willingness to appease her and the Third Reich after Archer slays their officer, but doesn't seem to care for any of these things on a personal level, instead merely playing the role required and shows a preference for hunting down an opposing Master rather than a Servant. He is also prejudiced against people who aren't born fully Japanese and hates foreigners since he mistreated Kaname due to being born half Japanese and half foreigner. He doesn't care about saving lives, and doesn't mind sacrificing several citizens who aren't even mages or soldiers in order to win the war.
He is seen observing Archer as she destroys enemy bombers before demanding her Master recall her. He thanks Archer for saving Japan, but she berates him and his officers for leaving Japan vulnerable in the first place, then commands the officers to seize the surviving bombers that made emergency landings. He suggests hunting down Saber and her Master, but Archer dismisses him. When asked what to do about the Third Reich representative Master that Archer killed, he orders that the body be sent back to the German Third Reich with an apology for their Servant's actions.
The next day, he sends soldiers after Saber's group, saying he doesn't care that they are Japanese; they oppose him so they are traitors and deserve death. He declares that his group will get the Holy Grail in the end and he doesn't care about the wishes of the Servants as they are already dead. The soldiers he sent are cut down by Saber and Assassin.
He is assigned to be an escort to an unnamed Japanese minister after the current situations in a war. He asks him about his thoughts about fighting on the mainland, and when the minister says to keep fighting until the last man standing, Magatsu replies he believes that they should surrender due to the country being low on food and that they don't have enough iron. The minister asks him if he was major, but Magatsu says he's not from the military. He explains it is top-secret and he was appointed to the army two years ago after he joined a secret unit tasked with researching supernatural powers. He offer the minister a cigar, adding that he's the kind of person who would find honor in dying in front of a desk rather than in front of an enemy. When the minister says not everyone in the army think the same, he says he loves his country and the reason he came to him with the proposal to fully prepare execution. After his talk with the commander, he says he should've have had him take care of the war.
Back to headquarters, Major Magatsu falsely reports to his men that the minister was assassinated by the driver who committed suicide. He encourages them to make preparation to fight on the mainland and makes them think it was the minister's will. He states it is the army's duty to protect their country and claim victory. After the meeting, he meet up with Archer's Master, Kaname, about the situations on Saber's Master and her Servant. He later orders Kaname to put together another team to attack Saber's faction even though it meaningless. He knows what Kaname's thinking that "it doesn't matter how many men they sent, they will never be able to kill a Master as long as the Servant is around." Magatsu's real plan is to exhaust both Saber and her Master until they can no longer fight back. He slaps Kaname hard after she attempts to mutter an objection. He threatens her that, if she disobey his orders, he will punish her. When Kaname still hesitates to send more men into battle against Saber's faction, he decides to send troops who are willing to volunteer. He secretly meets up a member of German Third Reich who is the Master of Assassin, Major Reiter, as a symbol of their new alliance. He makes a new plan to send his Berserker into the battle and war.
He informs Major Reiter about the current situation on Archer's condition after her fight with Saber. He is planning to use Archer to fight on the mainland against the Allies since she was the winner from the previous Holy Grail War two years ago. He is not planning to give the holy grail to Archer once she wins both wars and he is thinking of getting rid of her afterwards. When Major Reiter asks if he's planning to use a Command Seal to make Archer commit suicide, he says he isn't sure since she might trick her Master into using all of her Command Seals and get a new Master. He states he will make sure Archer fights in the mainland in order to protect their country. He believes sacrificing several citizens (who aren't even mages) will be a worthy sacrifices in order to achieve victory. After his conversation with Major Reiter, he reminds her that their alliance is temporary and bid her farewell.
He asks Kaname if they found Saber and her Master, but they haven't found them yet. He orders Kaname that they need to investigate other Masters and tells her not to slack off in the search. He notices someone wrote a quote that says "When the madman runs, any man not mad starts running". When Kaname asks if he wants to have take the banner down, he tells her to leave it since he likes it. A soldier reports about how their special attack aircraft dealt a fatal blow to one of the enemy battleships. He gives a pack of cigarettes to the unnamed soldier and claims there are herbs inside of it. He orders the soldiers to tell to the army, "All of us have nothing but the utmost respect for those of you who give your life for our country. Go on become Heroic Spirits, and protect us..." This leaves the soldier crying and moved by Major Magatsu's words. Afterwards, he notice the troops has got stronger every day and hopes if they succeed in the coup and take control of the government, fighting the war in Japanese soil will become a reality. In his thoughts, Magatsu's real goal is to create a world where magi stand at the top and wants to make his dream into a reality with only those with power should gain power. He talks to Kaname about the soldier, calling him an idiot and finding his face with snots coming out hilarious.
After receiving a report of a new Servant and ordering more information to be gathered, he stumbles upon some of the soldiers disciplining (i.e. beating) one of the survivors of the squad sent after Saber, calling him a coward for being too scared to face a Servant again. Full of patriotic fervor, they proclaim to Magatsu that they are eager to go on the battlefield and know he is the one who will save Japan, to which Magatsu silently muses to himself that he should adjust the dosage of their brainwashing tobacco. Later, he receives Kaname's report that the Heroic Spirit Restraining Device will undergo its activation test in two days. When he notices Kanata Akagi's hourglass, Kaname says that Archer found it, adding that she can tell it is special and would like to find out how it works. He replies he doesn't care and berates Kaname for wasting his time instead of doing her job of reporting Archer's movements to him and finding the whereabouts of the previous Grail. He further taunts her as he reminds her that he was the one who saved her life two years ago, that the reason she became Archer's Master was on a whim, and he blames the soldiers' deaths and punishments on her. His verbal abuse is interrupted by the arrival of Archer, and he panics, thinking she will kill him for displeasing her, but she ignores him and simply tells him that she will show him what she's been up to the next night, leaving Magatsu fuming at her disinterested attitude.
Later that night, he takes a few men with him to sneak into a laboratory of the 4th Magecraft Division held by Archer without her knowing, taking advantage of her absence dealing with bombers. They find that she is turning the Holy Grail into a bomb.
He decides to release Berserker from his tank and orders him to bring that "brat's" head to him. He witnesses his Servant starts slaughtering his men, he orders his men not to shoot. Major Magatsu panicked and tries to order him to stop, but he didn't listen. He begins to realizes something was off and the restraining service isn't working on his Servant. Major Magatsu attempts to use his Command Seals to make his Servant kill himself, but Berserker quickly cut off his right arm. He screams in agony after losing the arm that contains his Command Seals. He reacts in shock as his Servant destroys his detached arm. He hesitated and asked him if he is not Miyamoto Musashi, his Servant responds he is Musashi, the demon Musashi. He is later being carried around by Berseker as he continues slaughtering soldiers. He begged anyone to stop Berserker. 
Magatsu is a shrewd officer, savvy in both tactics and politics, as he is aware of the advantage they should press against Saber and the effect Archer's actions may have on the Japanese alliance with the Third Reich. He relies on manipulating others, using nationalistic rhetoric to invigorate his subordinates, and making use of cigarettes and cigars laced with magical herbs to influence people.
 Fate/type Redline - Volume 2 - Glossary: Major Magatsu [Master], p.203
Major Magatsu [Master]
A consultant magus from the Imperial Army. 24 years old. He comes from a family of magi who specialized in ancient magecraft to communicate with dead spirits. Due to the current Holy Grail War, he was especially invited into the Army. Unlike Fujimiya, he’s a magus from a family with far greater history and pedigree, but Magatsu himself seems to prefer climbing up the ladder of normal society rather than that of magi society.
- Fate/type Redline - Chapter 8.1
- Fate/type Redline - Chapter 12.1
- Fate/type Redline - Chapter 15.1
- Fate/type Redline - Chapter 15.2
- Fate/type Redline - Chapter 9.1
- Fate/type Redline - Chapter 3.2
- Fate/type Redline - Chapter 8.2
- Fate/type Redline - Chapter 3.3
- Fate/type Redline - Chapter 9.2
- Fate/type Redline - Chapter 13.2
- Fate/type Redline - Chapter 15.3
- Fate/type Redline - Chapter 15.4