Wall of Wood
The shimmering object finally resolved itself into solidity before hitting the ground with a solid thunk. It was an ordinary mundane spear, wooden shaft and all. Lancer blinked at the sight, perhaps rarer than swords that shot beams.
Body moving by instinct, he thrust experimentally over the spear on the ground, but it lay still as his attack was parried. As Lancer's weapon returned to him, the fallen spear shimmered away into nothing. There was no way to tell what Saber would have done with it had he stayed close-in earlier.
His blood was still up, guiding him into a flurry of quick thrusts, some feints but mostly genuine attacks. Now, Saber seemed even less inclined to meet him directly, constantly backing up rather than go for the parry. Taking or losing ground hardly meant anything with their speed, but each small retreat left Lancer's spear maddeningly close to any contact. It was as though she was trying to-
He quickly reversed his advance as a now-wall of green shimmered briefly, depositing over a dozen more spears into the air. With the tip of his weapon, he caught one mid-fall and flicked it back at Saber, who didn't react as it simply disappeared.
"Did you learn from Teacher too? I'd complain about her teaching a Saber spear techniques that I didn't get, but I guess you qualify for the Lancer class too, am I right? Well my uncle has a massive drill sword that he claims 'counts as a lance'. Come of think of it though, does Teacher throwing copies of her spear mean she can be an Archer? Oh wait, she can't be a Servant, I think."
Not pausing mid-sentence, Cu Chulainn spun his spear about as Saber, like he predicted, brought up more spears and threw them at him.
He received a small shock on realizing that the projectiles did not seem to trigger his Protection from Arrows skill. Some of Saber's spears simply blurred -through- the circle protected by Lancer's red one, but they also passed through him harmlessly. The sound of them hitting the ground behind him meant that...!
Both sides came to the same conclusion, at the same time. Saber's spears, unlike the one's that Lancer's Teacher used, took some time to materialize. And she only just realized it herself. Shouting in excitement, Lancer charged though a new shimmering array of weapons.
His spear slammed into a large round shield and bit deep. Both sides froze, Saber looking at the spear that had nearly effortlessly pierced her large bronze-covered aspis shield. Lancer quickly pulled back, a sudden need to retreat momentarily seizing control as he realized -something- had happened to his Master. He heard Saber mutter something as hundreds more of her shield flashed into being between the two combatants.
She could calmly admit to herself that she was in a really bad spot. The shield was only a normal shield, mass produced during the time of Agesipolis III of Sparta. Even if it was one of the heaviest mundane shields, it wouldn't do anything against a weapon on the level of a Noble Phantasm. She peeked around carefully and saw Lancer looking like he'd just seen something horrifying, maddening or both.
Thinking quickly, she muttered the line to activate ((Thousand Layered Shields)) on the one she held, filling the air with exactly a thousand "copies" of the frail thing. It was time to run, Lancer was shouting something, probably about to activate his Noble Phantasm. She turned around, without any sense of shame at running away. It was time to lea-
Though Cu Chulainn could not see though the shield wall in front of him, it hardly mattered if he could. That might be Saber's Noble Phantasm, but probably only a skill, since she was after all a heroic spirit of the sword. He didn't know if she had a better ranged attack, like a holy sword's beam, if she would use it while he retreated if she did, and if he could dodge or otherwise Protection from Arrows from it if she did.
He really didn't like the feel of being ripped apart by a magical energy beam.
It only took him a moment to make up his mind. Even though he might need as much magical energy as possible, this use of his Noble Phantasm was quite efficient. And, sword beam or not, leaving a powerful Saber at his back was never a good idea. Sending his bloodlust and mana into the spear, he felt himself growing calm as it practically lit up, whining with the desire to pierce.
"Your heart is mine!"
He couldn't see her directly, since she was using the shields as cover, but he could sense her well enough for the weapon's curse to activate. There was no escaping it now.
"Gae Bolg!"
Almost lazily, he pushed the point of his spear upwards toward the sky. Taking on a life of its own, Gae Bolg, the Barbed Spear that Pierces with Death ripped itself free from his hands, soaring up and above the mass of shields before stopping in mid-flight, flipping over to point downwards, and diving.
"- Bolg!"
She turned her head to see Lancer's weapon making as though to stab the moon, but paused as it suddenly disobeyed the usual laws of physics to stop and turn about to point at her. She froze, but it wouldn't have helped even if she had the presence of mind to try dodging or taking out another shield.
The blood-red weapon darted towards her. Her red blood soon splattered over the its barbed spearhead.
Cu Chulainn smiled in slight disappointment as his weapon somersaulted over the shields, returning eagerly to his hand, wet with Saber's heartsblood. Though the shields were still standing solidly, there was no need worry about Saber. The moment he unleashed Gae Bolg via its True Name, her heart being pierced was already inevitable. Even if she had an excellent level of Battle Continuation, it wouldn't allow her to both pursue and overcome him.
He turned to leave.
Master, you better not die on me.
.
Notes:
And first blood goes to Cu. Gae Bolg is really cool. Since it's apparently a very energy efficient Noble Phantasm, he really should use it more. Compare with say Fate/Grand Order Medea who uses her Rule Breaker like she's going knife yandere on someone. (I love both NP animations by the way)