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.
Fate/Accel Zero Order -Lap 2-
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.
Mana Burst (Leap) (A):
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.
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.
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 Fate/Grand Order - Profile of Diarmuid Ua Duibhne (Saber)
 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.