Cu Chulainn is an Irish mythical hero who appears in the stories of the Ulster Cycle, as well as in Scottish and Manx folklore. The son of the god Lugh and Deichtine (sister to the current king of Ulster), he was originally named Setanta, but gained his better-known name as a child after he killed Culann's fierce guard-dog in self-defense, and offered to take its place until a replacement could be reared. Cu Chulainn trained in war under the goddess Scathach, who lives in the Land of Shadows, and earned the magic spear Gae Bolg. At the age of seventeen, he defended Ulster single handedly against the armies of Queen Mab of Connacht in the epic Tain Bo Cuailnge. It was prophesied that his great deeds would give him everlasting fame, but that his life would be short; one reason he is compared to the Greek hero Achilles. He is known for his terrifying battle frenzy, in which he becomes an unrecognizable monster who knows neither friend nor foe. He fights from his chariot, driven by his loyal charioteer Laeg, and drawn by his horses, Liath Macha and Dub Sainglend.
Many say he acquired a lot of power by submitting himself to some geis, two of which are "I'll never eat dog meat" and "I'll never refuse a meal offered by a woman." But then a woman offered him some dog meat, as so he had to choose what geis to break and he accepted the meal. After that, he was forced by Mab to break his geis one by one, as so he met his death at the hands of Lugaid (child of Cu Roi, a man he had to kill to defend Ulster). He once spurned the goddess Morrigan and was cursed to die by being pierced on his own spear. Afterwards, Morrigan took him to the land of the fae, where he became a knight.
"Origin: Ireland. The legendary fairy hero. He was a beautiful young man once, with dauntless courage. He is the son of Lugh, the god of light. He took on a dreadful form in battle and fought with a powerful spear, the Gae Bolg. He spurned Morrigan and was cursed to die by being pierced on his own spear. Afterwards, Morrigan took him to the land of the fairies, where he became a knight."
—Shin Megami Tensei A-Mode DDS dictionary
Shin Megami Tensei III: Nocturne
Cu Chulainn appears as a distinct demon. He cannot be encountered nor recruited by the Demi-fiend, rather, the Demi-fiend can only obtain him by evolving Setanta by reaching at least Lv. 52 himself and completely mastering Setanta's skillset.
Shin Megami Tensei IMAGINE
"A demigod hero of Celtic mythology who originated in Ireland. He is the son of the sun god Lugh, of the Tuatha De Danann. His name means "hound of Chulainn" A strikingly handsome young man, Cú Chulainn was said to be dauntless and bold. When a battle begins, blood sprays from his pores, his jaw swells up to the size of his head, and his mouth splits open from ear to ear, giving him a terrifying appearance and causing his enemies to quake in fear. Cú Chulainn trained in war under the goddess Scáthach, who lives in the Land of Shadows, and earned the magic spear Gáe Bulg. Later, he broke the taboo (geis) upon him and grew weak as a result. Under a terrible curse, he finally met his demise pierced by his own spear. Some suggest that Cú Chulainn was a real historical figure, and today there exists a stone called the "Stone of Cú Chulainn," to which the hero is said to have tied himself in his dying moments."
—Shin Megami Tensei IMAGINE compendium
Cu Chulainn can only be obtained through fusion. He acts as a boss with Morrigan within Shibuya's Quartz gold level instance and plays a central role as an NPC and enemy in the Foreign County in the Woods series of quests.
He is one of the demons it is possible to obtain as a mount. When the player uses him as a mount, he carries the player bridal style regardless of player gender. His armor appears as equipment for the player along with an all-black variant. It is also possible to acquire his spear, Gae Bolg, which grants the ability to use a penetrate affinity skill by the same name when equipped. Gae Bolg can be obtained by using the care command on the demon or through synthesis.
Through a series of G1 Trial quests from a Cathedral of Shadows researcher in Ikebukuro, it is possible for players to fuse a strengthened version of Cu Chulainn that learns his unique skill Gae Bolg as well as has increased HP cost reduction.
Shin Megami Tensei: Strange Journey
"A gallant Celtic hero, son of the sun god Lugh. He is said to have beaten an army singlehandedly. He was cursed to die after spurning the war goddess Morrighan, and was impaled on his own mighty Gae Bolg."
—Shin Megami Tensei: Strange Journey compendium
Cu Chulainn appears as an NPC in the EX Mission "A formal search request," in which his mother has traveled to the Schwarzwelt to find him. The trail for him leads first to Sector Bootes, where an Orthrus will indicate he has moved to Sector Antlia to offer support to his old teacher Scathach. Meeting with Scathach will reveal Cu Chulainn has heard of the search and is moving to meet the protagonist.
Near the entrance to Sector Antlia, Cu Chulainn will be found with Enemy Search. He will leave for Sector Carina to meet with his mother; once met there, he will reward the protagonist by unlocking himself for fusion, giving him Gae Bolg and the item Knight's Oath, which contains a Demonica code to summon him.
Shin Megami Tensei IV
He appears in the Challenge Quest, Cu Chulainn's Training. His teacher, Scathach, has turned Cu Chulainn back into Setanta and wants 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.
Shin Megami Tensei IV Apocalypse
"A gallant Celtic hero, son of the sun god Lugh. He is said to have beaten an army singlehandedly. He was cursed to die after spurning the war goddess Morrighan, and was impaled on his own might Gae Bolg."
—Shin Megami Tenser IV Apocalypse compendium
Cu Chulainn can teach Nanashi the Floral Gust, Javelin Rain, Dark Sword and Critical Eye skills through his Demon Whisper. He benefits from learning Physical and Force skills.
Devil Summoner: Soul Hackers
"A gallant Celtic hero who wields the mighty spear, Gae Bolg. He is the son of the sun god Lugh and Deichtine and possessed formidable strength ever since childhood. In battle, his normally beautiful appearance turned fearsome and is said to have turned away an army on its own. He was cursed to die for spurning the war goddess Morrigan's love and was impaled on his own mighty Gae Bolg. Even then, though, he tied his body to a pillar and died without ever falling."
—Soul Hackers 3DS compendium
Cu Chulainn appears as the Persona of the Tower Arcana. He can be summoned once the protagonist reaches Lv. 40 or above. Cu Chulainn, along with Scathach, also grants the protagonist the Fusion Spell Shadow Hound, which inflicts severe Strike damage upon all enemies.
Cu Chulainn returns as the Persona of the Tower Arcana, retaining all of his attributes. However, as FES introduces the weapon fusion system, Cu Chulainn can be fused with any Nihil item into a distinct weapon at the antique shop via the Weapon Fusion system. The weapon is Gae Bolg, a spear holding 260 ATK, 85 Accuracy and the passive ability Wind Amp. Gae Bolg inflicts Wind-based damage via Wind Attack upon striking enemies with it, rather than dealing Pierce Attacks.
During his confrontation with the Phantom Thieves in Shido's Palace, Goro Akechi summons Cu Chulainn and Cerberus to demonstrate his ability to induce madness in whomever he pleases. Cu Chulainn will attack the party with highly damaging Physical skills until he and Cerberus are defeated, upon which Akechi will continue the fight unaided. As a Shadow, Cu Chulainn is known as the "Spear-wielding General."
"A hero in Celtic folklore. He was called Setanta until he earned the name, "Culann's Hound." There are many tales of his adventures. He received his spear, Gae Bolg, from his mentor, Scathach."
—Persona 5 Strikers background
Cu Chulainn is a Persona of the Star Arcana and can only be obtained through fusion in the Velvet Room. He is the subject of the "Prison Mail, Part 8" request for Lavenza, in which she requests to see a Cu Chulainn with the Concentrate skill. Leveling Mot to level 59 so he learns Concentrate and then fusing Mot with Nebiros will allow Cu Chulainn to easily inherit the Concentrate skill.
DemiKids Light & Dark
"An honorable and trustworthy demon-knight armed with his mighty lance, "Gaiborg"."
Known as Karfu, he can perform the combo Razor Dance with Scatha, Zypher or Roog and Holy Slash with Tamlin. He also has the power Odds Breaker.
Digital Devil Saga: Avatar Tuner
Cu Chulainn appears as a normal enemy encounter. He can easily be found at Coordinate 136. Optionally, after defeating Mick the Slug, the party can return to Coordinate 136 where they will find the remaining HipHop Brother, Pyro Jack. Should they choose to help him find the key to open the chest, a Cu Chulainn will appear. Talking to him will net the player a key but it will not open the chest. He is also one of the demon allies summoned by the optional boss Demi-fiend during battle; he focuses on lowering the party's Defense and striking them with powerful Physical attacks.
Digital Devil Saga: Avatar Tuner 2
Cu Chulainn returns as a normal enemy encounter in Digital Devil Saga: Avatar Tuner 2. He can easily be found in final dungeon, the Sun. Cu Chulainn often appears alongside with Pallas Athena when fought.
Cu Chulainn is a demon of the Genma race and can be fused once the protagonist reaches level 39. As a unique demon, only one Cu Chulainn can be possessed by the party at a time. Cu Chulainn is one of only a handful of unique demons (including Shiva and Norn) to appear in free battles, consistently appearing on day 6 and 7.
Devil Survivor 2
"A gallant Celtic hero who wields the mighty spear, Gae Bolg. He is the son of the sun god Lugh and Deichtine and had mighty strength ever since childhood. In battle, his normally beautiful appearance turned fearsome and is said to have singlehandedly turned away an army. He was cursed to die for spurning the war goddess Morrigan's love and was impaled on his own mighty Gae Bolg. Even then, though, he tied his body to a pillar and died without ever falling."
—Devil Survivor 2 compendium
Cu Chulainn returns using his old design from Soul Hackers which makes him and Tam Lin no longer share the same, palette-swapped appearance.
Shin Megami Tensei: Liberation Dx2
"A gallant Celtic hero, son of the sun god Lugh. His weapon is the mighty spear Gae Bolg. His good looks could be deceiving, for in battle he is ferocious, tearing down his enemies and wiping out their armies."
—Shin Megami Tensei: Liberation Dx2 compendium
Cu Chulainn is a fusable 5-star demon. He has the unique skill Gae Bulg as a physical attack and is the only fusable demon who learns a passive elemental pierce skill, namely Force Pierce.