Scathach ("Shadowy") is a figure in the Ulster Cycle of Irish mythology. She is a legendary Scottish warrior woman and martial arts teacher who trains the legendary Ulster hero Cu Chulainn in the arts of combat. Texts describe her homeland as "Alpi", which commentators associate with Alba, the Gaelic name of Scotland; she is especially associated with the Isle of Skye, where her residence Dún Scáith (Fort of Shadows) stands.
Scathach's instruction of Cu Chulainn appears in Tochmarc Emire (The Wooing of Emer), a foretale to the great epic 'Táin Bó Cúailnge'. Cu Chulainn and Emer fall in love, but her father Forgall forbade the union until Cu Chulainn has completed his warrior training. Cu Chulainn and his friend Ferdiad travel to Dún Scáith, where Scathach teaches them feats of arms, and gives Cu Chulainn his deadly spear, the Gáe Bulg.
Cu Chulainn begins an affair with Scathach's daughter Uathach, but accidentally breaks her fingers. She screams, calling her lover Cochar Croibhe to the room. Despite Uathach's protests, he challenges Cu Chulainn to a duel; Cu Chulainn dispatches him easily.
To make it up to Uathach and Scathach, Cu Chulainn assumes Cochar's duties, and becomes Uathach's lover. Scathach eventually promises her daughter to him, without requiring the traditional bride price. Scathach also grants Cu Chulainn the "friendship of her thighs" (they have sex) when his training is almost complete. When her rival, the warrior woman Aífe, threatens her territory, Cu Chulainn defeats her in battle and forces her to make peace. Aífe also sleeps with Cu Chulainn, producing his son Connla, who Cu Chulainn kills years later without realizing he is his son.
"A great warrior and prophetess of Celtic mythology, also known as 'The Shadowy One'. She taught Cu Chulainn martial arts and gave him his famous spear, Gae Bolg. Her sister is Aife."
—Shin Megami Tensei III: Nocturne Compendium
Scathach can evolve into Skadi by leveling up. She also appears in the Bandou Shrine as a regular enemy, though she is unable to be recruited.
Shin Megami Tensei IMAGINE
"The Lady of Shadows and teacher of Cu Chulainn. famous for having given him the spear Gae Bolg. Scathach is a wizard also skilled in the martial arts, and many have headed for the Land of Shadows to receive her training. She has two sons, both of whom are expert fighters. Although considered the top wizard-fighter in the Land of Shadows, her twin sister Aife is said to be her equal in combat. The Lady of the Lake from Arthurian legend is said the be based on Scathach."
—Shin Megami Tensei IMAGINE Compendium
Scathach is a central figure in the Foreign Country in the Woods series of quests. She also appears as support for Thor when he acts as a boss in Celu Tower's gold instance.
Shin Megami Tensei: Strange Journey
"A warrior queen of the Land of Shadows in Celtic lore. She taught the Irish hero Cu Chulainn the art of war, and gave him the spear Gae Bolg."
—Shin Megami Tensei: Strange Journey Compendium
She appears as a summonable demon and as a NPC in Sector Antlia, in Morax's old lair, as part of the EX MissionA formal search request, in which she received the help of Cu Chulainn in one of her endless battles. She expresses her appreciation for her student, though she chides him for believing she needed his help in the first place. She tells the Protagonist that Cu Chulainn heard of the search for him and that he now was searching for the Protagonist himself.
Shin Megami Tensei IV
The client of the Challenge Quest, Cu Chulainn's Training. She has turned Cu Chulainn back into Setanta and asks Flynn to face him so he learns the way of the warrior. After learning the lesson, she restores Setanta back to his original form and thanks Flynn.
Devil Summoner: Soul Hackers
"The war goddess of Celtic lore, as well as the queen of the Land of Shadows. She is a skilled magician and a master warrior. She trains young men who come to her in the art of war. The famed Cu Chulainn was one of her students, and it is said that he received the legendary Gae Bolg upon his mastery of her teachings."
—Devil Summoner: Soul Hackers 3DS Compendium
If Scathach is used in Sword fusion, she will transform into the special weapon Gae Bolg.
Devil Children Red/Black Book
Scathach can be obtained by rank fusing Tsukuyomi nine times.
DemiKids Light & Dark
"A queen of the nether realms, this caped demon is a master of weapons."
Known as Scatha, she can perform the combo Razor Dance with Karfu and Holy Flash with Doom Cat.
Devil Children Messiah Riser
Scathach is a general of the Imperium army and appears alongside the other Generals near the beginning of the game. She later shows up in Center Makai, where her forces have taken over. Scathach is fought in the Dark Palace and puts Jin, Rand, and Lena to sleep on Akira's route before the battle. After losing she unleashes a fire attack that knocks Jin and his group out, leaving Akira to go on ahead.
She is then found in the deeper part of the Dark Palace with the dark seal, and makes Akira's partner Gale vanish. Scathach demands that he use the crystals to destroy the seal in exchange for his partner, which he does, freeing her master Gaap. Once free, Gaap kills her since she served her purpose.
Devil Survivor 2
"The war goddess of Celtic lore, as well as the queen of the Land of Shadows. She is a skilled magician and a master warrior. She trains young men who come to her in the art of war. The famed Cu Chulainn was one of her students, and it is said that he received the legendary Gae Bolg upon his mastery of her teachings."
"I am Megami Scathach, queen of the Land of Shadows... I shall guide you to victory."
"You continue to strive for power. As you should."
Gallery
Artwork from Persona 3
Artwork in Devil Children Red/Black Book
Model in Shin Megami Tensei III: Nocturne
Scathach as she appears in Shin Megami Tensei: Strange Journey
Portrait from Shin Megami Tensei: Strange Journey
As she appears in Devil Children Messiah Riser
Scathach as she appears in Card Summoner
Scathach as she appears in Devil Survivor 2
Scathach as she appears in Shin Megami Tensei Gaiten Hato no Senki
Scathach as she appears in Raidou Kuzunoha vs. The Lone Marebito
Scathack as she appears in Persona 4 The Golden Animation
Trivia
Contrary to popular belief, she is wearing a mask proven multiple times throughout the series like in Shin Megami Tensei IMAGINE when she is among other demons being the only one who doesn't move her "mouth" when she speaks. To date, she is never seen without her characteristic mask.
