As a Caster, he does not put on any metallic equipment.
Having manifested as a Caster, he apparently has imposed upon himself the role as one who guides. Not as a true druid, but as a temporary one, as long as he continues together with his master, he shall illuminate the path that the Master walks on.
- Lancer (Cu Chulainn)
- Caster feels miserable whenever Lancer mocks him for being a "spearless me."
- Caster has a tendency to make remarks about Mash's body, complimenting it and saying the view of her behind "is nice."
Fuyuki: Contaminated City in Flames
He appears in the "Burning pollution city Fuyuki singularity F". He assists the Ritsuka Fujimaru and Shielder, helping them defeat the other Servants serving under Artoria Alter and providing advice for them. After all of the other Servants are defeated, he also disappears, telling the Protagonist and Mash to summon him as a Lancer next time.
In the First Order movie, Chulainn had already defeated both Hassan of the Cursed Arm and Darius III, before meeting Ritsuka Fujimatu and Mash. He also battles EMIYA alone, managing to beat him in a close battle, and delivers the final attack to Artoria Alter with his Noble Phantasm, Wicker Man.
Boundary of Emptiness: Garden of Order
In his interlude Sage of the Forest, Cú Chulainn senses a distortion in a forest in Britannia, but Romani doesn't get any readings. After defeating werebeasts that appeared, Cú Chulainn speaks about his abilities that were given to him as a druid when he was summoned as Caster. The source of the distortion, the ghosts of druids, then appear, but they're soon destroyed by the group. With the distortion gone, Ritsuka asks Cú Chulainn if he wants to visit Ulster, but he refuses as he doesn't disturb them with his sudden return.
Having manifested as a Caster, he underwent a sudden change from when manifesting as a Lancer and now torments his opponents as a user of diverse Magecrafts. He has powerful heat・flame attacks as his specialty. Apparently, the "ansuz" rune is being employed in this.
Rune Magic (A Rank): Possession of the Magic Crest of Northern Europe - the runes. By making proper use of this, powerful and varied effects are mastered. However, simultaneously employing multiple effects (joint use) is inadvisable.
He is also known as the Prince of Light (Provisional Caster) (光の皇子（暫定キャスター）, Hikari no Ōji (Zantei Kyasutā)?) in Fate/GUDAGUDA Order.
Mata is the character illustrator for the Caster version of Cú Chulainn.
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