A strong knight who makes full use of the two demonic spears and two demonic swords. As the Fairy kings, the God of Love Aengus and the Sea God Manannán raised him, he is an unequaled handsome man. Under the leader Fionn mac Cumhaill he was the greatest knight of the Knights of Fianna and his great efforts in the common front of the Knights against Fairy King Abarta are often told of.
According to an anecdote, when going into life-threatening adventures, Diarmuid carried around the demonic sword Moralltach and demonic spear Gáe Dearg, when danger was scarce it's said he decided at that time to hold the demonic sword Beagalltach and the demonic spear Gáe Buidhe in his hands. At his time of death Diarmuid the equipment he carried was the latter. Had he entered the mountain with the former equipment, to bring down a demon boar, the strongest knight of the Knights of Fianna might have had a long life.
As for now, he's existing with a Saber’s Saint Graph in the present world. The other him only utilized the spear, now he prides himself also in the sword, but... This Saint Graph emphasizes more his aspects as a "hero of legends and myths", and, maybe because he possesses multiple Noble Phantasm that are the hands of God, his difficulty/cost for summoning is higher than when he is a Lancer.
Serious loyalty, endowed with faithfulness, a noble Heroic Spirit. Fundamentally a Lancer at one time, he is the very same person but summoned as a Saber, but as a "Knight" he attained especially strong self-awareness. Enjoying the fight with a strong enemy, wishing for himself not to hesitate. Furthermore, whether he is aware of it or not, his self-esteem is quite stronger than when he is a Lancer.
Event: Sparrow's Inn Daily Report
Sion Eltnam Sokaris arranges for Diarmuid andFionn mac Cumhaill to be Goredolf Musik’s bodyguard while he and the others stay at a Japanese hot spring escort in a harmless Singularity as part of an experiment to test Novum Chaldea’s rayshift capabilities. Unfortunately, Diarmuid, Fionn, and Goredolf arrive away from the rest of the group. The three are lost in the mountains for three days until they find and enter the Enma-tei through its open backdoor. Arriving in the Tribute Hall, they find a mountain of food and an offering box. Diarmuid and Fionn immediately start eating the food, not understanding it’s an offering to the gods. Goredolf, meanwhile, is far more cautious and pleas for the Celts to stop eating but is ignored. However, he opens the offering box after Chief Snake convinces him to.
Beni-enma and the others soon arrive, having heard there were “bandits” from Chaldea are raiding the Tribute Hall. Beni-enma explains the hall is the heart of the Enma-tei and dedicated to all the Shinto gods. The offering box contained all the previous year’s gratitude (QP) collected from the guests who finished their stay. Once a year’s worth is collected, it is customary to convert it through ritual prayer and offer it up to the gods of Izumo so the next year will be safe and peaceful. But with it now free, Beni-enma warns the Chaldeans they cannot leave as the gods will punish them if they do. She explains if they fail to replenish the lost gratitude before the offering day, which is in two weeks, they will all be turned into pigs. She can’t help as it must be gathered by those who lost it and cursed in the first place. Her only advice to them is to work, explaining gratitude is collected from all living things staying at the inn every day. If they can ensure the other guests are happy and satisfied, they may increase the gratitude collected. Beni-enma then has Toshi escort the group to their rooms.
After they all see their rooms, the Chaldeans meet in Ritsuka and Mash’s room to discuss how they can go about collecting gratitude. Tamamo-no-Mae recommends they each do tasks they know they can handle while getting understanding of the inn’s innermost workings. On that note, Fionn says he learned from the sparrows that there are three major jobs that need doing. First: procure fresh high-quality ingredients from the mountain and river; Second: procure lumber; Third: drive away the demonic monkeys who have been causing mischief as of late. Diarmuid and Fionn both agree that the third task is most suitable for them.
Despite all their hard work, the Chaldeans receive not a shred of gratitude. They determine the inn needs new guests, as the only other guests have been staying for years and their offerings have been getting increasingly smaller with their lives becoming routine. Fionn suggests attracting Heroic Spirits to the Enma-tai through their bonds and advertising. For advertising, though, they’ll need first fix the inn up. Tamamo recommends they start off with renovating the other guest rooms. Sasaki Kojirou later becomes the first new guest of the Enma-tei.
The next morning, Diarmuid reports the monkeys have been engaging in mischief on a wider scale than previously thought. They attack the sparrows throughout the mountain and interfere with their collecting of fresh ingredients from the mountain and river. Kiyohime adds the monkeys have also been causing trouble in the inn itself. Ritsuka, Mash, Diarmuid, Fionn, and Tamamo later go hunting with Beni-enma.
On another morning, Ritsuka and the others are having tea when Tamamo barges in to inform them of the huge influx of new guests. While Tamamo and Tamamo Cat help Beni-enma in the kitchen, Ritsuka and the others serve the guests in the Phoenix Hall. Diarmuid entertains the guests by juggling five daikon radishes with his swords. Beni-enma and the sparrows later take over for Ritsuka and the others.
The next morning, Ritsuka and Mash inform the others that Beni-enma has been using the collected gratitude to repay interest to the Bamboo Cutter, who five hundred years ago demanded compensation for the theft of his five family heirloom. Fionn says they need to resolve the debt before the Bamboo Cutter sells the inn, otherwise, they’ll all become pigs. Goredolf recommends finding and returning the Bamboo Cutter’s missing treasures to him, but Tomoe points out the issue that the theft took place 500 years ago. Fionn agrees with Goredolf’s idea, however, and suggests bringing back items identical to the Bamboo Cutter’s missing treasures. He suspects the Servants may have the treasures they require. However, he still wants them to restore the Enma-tei to its former glory, wishing to see the view from the castle keep.
The Chaldeans eventually collect the items they needed and restore the Enma-tei’s keep. In the keep, Fionn uses Fintan Finegas to determine what the room looked like 500 years ago. He also easily deduced who the culprit was, though he notes the difficulty of proving it. Also, even if they give the Bamboo Cutter the treasures they collected, Fionn is certain the Bamboo Cutter will counter that the treasures have to be the very same ones stolen from him 500 years ago. He therefore believes the Bamboo Cutter never wanted compensation and has been running a scam to get his hands on the Enma-tei. So they’ll need to counter cunning with cunning, which is why Fionn asked everyone to come to the keep to add the finishing touches. Then, after confirming with Kiyohime about her ability to sense lies and Beni-enma’s duty to punish lies, he tells everyone that they’ll be doing a con.
The day the Bamboo Cutter comes to collect arrives with everyone gathered in the entrance hall. The Bamboo Cutter immediately demands 100 billion QP for last year’s interest, refusing any excuses from Beni-enma about her inability to pay him back. As she can’t repay the interest, he seizes the Enma-tei and asks everyone to leave his property. But the Chaldeans then claim to the Bamboo Cutter that they found the heirlooms that were stolen from him 500 years ago and take him the very room he stayed at: the Raven Room.
There Goredolf claims they’re now in the Enma-tei as it existed 500 years ago as per Fionn’s “ability” to manipulate space-time. He then directs him to retrieve his heirlooms from the pouch on the table, warning doing so would mean he was the true thief all along. The Bamboo Cutter opens the pouch and laughs at the Chaldeans for thinking they tricked him into believing they traveled back in time. Because if they did, the pouch would be empty, as he never brought any heirlooms with him. Realizing what he just said, he has Moneyed Monkey recall what he witnessed back then. Monkey claims he saw the heirlooms, but Kiyohime senses he is lying. He can’t even describe one distinctive feature of the heirlooms. Kiyohime then senses the Bamboo Cutter is lying about having brought the heirlooms to the Enmai-tei. Before Ritsuka could even blink, Beni-enma cuts off the Bamboo Cutter’s mask. The Bamboo Cutter is revealed to have been the true Monkey in disguise and is the same monkey from the “The Crab and the Monkey“. Seeing the jig is up, Monkey calls Magistrate Tiger and Chief Snake over and they fuse to become Nue. He then jumps out the window and heads for the shrine. Figuring he intends to destroy it, everyone follows after him.
In the Tribute Hall, the group fight Nue. Afterward, to Monkey’s confusion, Tiger and Snake rebel against him, slowing Nue’s movements. They give their reasons for their rebellion and split from Nue, leaving Monkey behind. Beni-enma then finishes him off.
With the Enmai-tei freed of its false debt, Lord Enma allows the Chaldeans’ efforts to make amends to be used as the new year offering. The curse is thus lifted and the Chaldeans earn back the magical energy they collected as a Holy Grail. Beni-enma thanks them for all they have done, knowing the Enma-tei wouldn’t have been restored without their help. The Chaldean then hearing Sion’s voice coming from a Sparrow, who found the comm device Goredolf lost in the mountain when they arrived in the Singularity. Diarmuid is confused as he thought the reason Goredolf refused to contact Chaldea was because he was a brave and heroic commander. He asks Ritsuka if they knew, to which RItsuka confirms they did. Before they’re rayshifted back to Chaldea, Ritsuka wishes Beni-enma happy new year. Beni-enma responds that Chaldea and the Enmai-tei now have an undeniable connection, so if they ever need help, she’ll be happy to fight alongside them., though it might take a while to convince Enma to give his blessing. She then tells the Chaldeans that they’re always welcome. Fionn asks Diarmuid how his stay at the Enma-tei was, worried he gained nothing unlike himself. But Diarmuid, saying he couldn’t ask for a better reward than to see his captain demonstrate his valor. The Chaldeans are then rayshifted back to Chaldea.
During his interlude it is revealed in a flashback that he previously took part in an unknown Holy Grail War (presumably in London given Big Ben in the background) as a Saber class Servant. During this grail war he met Miyamoto Musashi, and during this encounter she informed him of Chaldea's existence and expressed a desire to see him there some day. He never forgot this encounter even after demanifesting at the conclusion of the grail war. This desire allowed him to manifest as a bug in the simulator.
Due to his presence the remnants of the Fairy King Ábartach's soul were drawn to him thanks to their deep connection and manifest in the simulator as some form of curse, or rather feelings that have degenerated into a curse. Ábartach's soul's desire to fight Diarmuid leads him to combat Yagyuu Munenori during a stroll in the simulator, their duel ends without either being being slain, this causes Yagyu to inform Kiyohime who then informs Ritsuka, Da Vinci, and Mash of the presence of an unknown non-NPC in the simulator, which prompts Ritsuka to enter to look for this non-NPC with the aid of Diarmuid's Lancer form at the latter's suggestion.
After entering, Diarmuid reveals that Yagyu didn't inform Ritsuka due to the a curse lingering on him after his battle with Ábartach's soul. This curse spreads to those he is near, and he choose to informed Kiyohime due to knowing she would have little difficulty dealing with the curse. The curse's effect manifested on Kiyohime as heaviness in the affected area, the shoulder, and it also was undetectable to the sensors in the Command Room of Chaldea. After revealing this Diarmuid remarks that he could smell "Danaan" on them.
After his first confrontation with Ábartach's soul, Diarmuid reveals he can't finish him off as a Lancer. Ábartach's soul remarks that Diarmuid is "not the one" and that his "spear is not enough" and demands that he be shown "the sword of Manannán" , referencing Móralltach, at which point Diarmuid's Saber, as a bug, appears and apologizes to his Lancer self, and informing him that Ábartach's soul is looking for both of them. However due to lacking a corporeal Spirit Origin he needs to make use of his Lancer self's, and requests permission to do so from Ritsuka. Lancer Diarmuid asks that Ritsuka grant his Saber self's request, to which Ritsuka agrees.
This causes both versions of Diarmuid's to resonate, changing the Spirit Origin to his Saber self. Ábartach's soul states why he manifested and challenges Diarmuid to a duel, which Diarmuid wins. This causes Diarmuid to recall why he manifested. After meeting with Holmes who mentions that their situation isn't dissimilar to Henry Jekyll and Hyde's case, albeit more temporary especially given how Saber Diarmuid's manifestation was due to his connection with Musashi. Saber Diarmuid's Spirit Origin is recorded into Chaldea's Database.
After enjoying himself around Chaldea for a while at the insistence of his Lancer self, Da Vinci and others, he then bids Ritsuka and Chaldea farewell and begins returning the spirit origin to his Lancer self. During his demanifestation, Artoria Pendragon appears and mentions how she regrets that they couldn't share a duel which Diarmuid agrees with.
The Saint Graph’s ability is higher compared to Lancer but, on the other hand, the degree of difficulty in summoning is also higher. The summoning person's ability needs to be better by far and, if special conditions aren't completed for the Saint Graphs materialization, it could vanish like mist.
During the times he was a Lancer, he also possessed Skills that were apparently sealed. In legends, it is said that Diarmuid chose to equip himself with one magic spear and one magic sword at a time, but just like how he was equipped with "paired spears" as a Lancer, he got "paired swords" with him as a Saber. Once he is summoned, there is no doubt that he will flourish as a powerful knight of the "two-sword style".
- Magic Resistance (A+ Rank): Nullifies magecraft spells that are Rank A or below. Modern mages would not be able to wound Diarmuid with their magecraft. It was originally Rank B, but it is being raised up to Rank A+ due to the effect of one of Diarmuid's Noble Phantasms.
- Riding (B Rank): One can freely handle all beasts and vehicles except the Phantasmal Species.
- Mana Burst (Jump) (A Rank): Raised by the gods, Diarmuid acquired superhuman jumping power. Manifesting as a Saber he possesses this Skill, but in exchange, his Agility parameter is lower than it was when he was a Lancer. He can explosively gain mobility by releasing mana, simultaneously improving his offensive ability.
- Honor of the Knights of Fianna (B Rank): Diarmuid’s unique resolution. Taking form as the strongest knight's mentality.
- Love Spot (B Rank): Seduces those of the user’s opposite sex by means of a beauty spot tinged with magical energy. A female who confronts Diarmuid will bear a strong feeling of love for him. Evasion is possible with the Magical Resistance Skill. Even if one does not have Magical Resistance, they can abate it to some extent so long as they maintain a will to resist. (His control over this Skill is effective under this Saint Graph in “Fate/Grand Order”.)
Diarmuid appears in the trailer for the fifth chapter of Fate/Grand Order, "E Pluribus Unum: The Grand Battle of Legends in North America". However, only his Lancer Class form appears in the actual Singularity.
- Fate/Grand Order - Profile of Diarmuid Ua Duibhne (Saber), translated by Kinalvin on Reddit
 ALL OVER/Zero - Fate/Zero Exchange of Questions and Answers, p.024
Questions 14: Is the reason Lancer didn't bring Moralltach and Beagalltach this time also because he (Kayneth) didn't listen to his wife? Would Beagalltach even be of use this time? [T]
Questions 14: Is the reason Lancer didn't bring Moralltach and Beagalltach this time also because he (Kayneth) didn't listen to his wife? Would Beagalltach even be of use this time? [ Ireland · Pig of Ben Bulben ]
Gen: Diarmuid is a nice guy who can read a situation. It would be a bit too much to bring out a sword as a Lancer. This time there was no advice from the wife. At the most she's just a fiancé. To Kayneth, that is.