There is no pain, but Archer has no reason to stay in this world, either.
Pain is a symptom of attachment to life. A body that still wants to live screams at its nerves mercilessly, begging the spirit within it to survive. Archer doesn't have to worry about that, even with his chest pierced and his arm now taken away. His spiritual core has degraded enough by now that he can't feel the agony those wounds should cause. Everything about him is resigned to disappear.
Or that's what he thought a moment ago, as the priest took his arm and attended to the boy. He thought that the only thing left for him to feel was the pull of the Grail on his battered spirit, that the only thing left for him to do was to surrender to the serious eyes and small hands of the white-haired girl watching from the corner. But now—
Ilyasviel almost pouts, but her gaze is too sad for that. "Why are you looking at me like that? You don't have much time, so you want to go to her, right? I'll take you when you're done no matter what you do. Go."
Archer says nothing to her. With so much stripped away from him, he can no longer speak to this reminder of the girl he could not save so long ago. Instead, he just nods, and he steps out of the room and heads for the chapel. He'll look at her one last time before he disappears. He'll fix her unconscious face in his heart, so he can have it with him in hell.
He has no sentiment for this rotten world any longer, and he could easily turn his back on most of it, but somehow Rin Tohsaka is an exception.
His remaining hand shakes on the door to the chapel, and it takes him three tries open it. The damaged vessel that is his body has almost stopped responding to his broken spiritual core. Still he hangs on. It's too much to think that he can touch her again, but if he could just see her face, he'll leave in peace. Archer pushes open the door.
And there his plan falls apart, because Rin Tohsaka stands in the middle of the chapel, swaying a little on her feet, her hair a bit messy around her pale face, her eyes bright and desperate.
"Archer," she says with a ragged voice, and even though he won't be able to keep his body from disintegrating for more than another few minutes, he can't leave, either.
So he smiles. For her, he smiles. "Wow, Rin, you're really a mess."
"You're really a jerk," she says. Tears have collected at the corners of her eyes.
"It's troubling that you're so sensitive," he says. He's too weary, too drained to beg her not to cry, so he keeps smiling. "I was only saying what I can see."
"It's not that," she says. A couple of tears spill over and trickle messily down her face. And she takes a deep breath and bursts out, "Stop fading, Archer!"
"Ah, I'm fading?" He looks down at the hand he has left. He can barely see the tips of his fingers. "I see. That's too bad." He says a rash thing, then: "I wanted to protect you some more."
"I have one more command spell," she continues. "I'll use it, because—I don't want to lose my Archer!"
He can't answer that with words. She's looking at him desperately, but they both know that even all three command spells wouldn't save him now. So he doesn't speak. He just walks forward to meet her.
Or he tries to, but as soon as he sets one foot in front of the other, Archer realizes that his feet aren't really there any more. He pitches down, onto his knees. The faint rustling of dust or sand comes to him as he lands, as more of his body dissolves away. He tries to lift his head to look at Rin, but it's so heavy, and his muscles don't want to work. He can only stare down at the floor of the church.
And then she's on her knees too, he's looking down to see her tear-stained face beneath his. He can barely feel them, but her hands are on his shoulders. "Why?" she says. "Archer, you still want to protect me…why? You've already given up everything for me, and um, I don't have any reward for you. I'm a really superior magus, of course, and naturally I'm beautiful a-and perfect! But I don't have anything, Archer. I don't have anything of my own except you, and I'm selfish, so I want to keep my Archer!"
Neither of them says anything for a moment. Archer laughs a little, weakly.
She glares at him. "Don't you dare laugh, Archer. Nobody heard me babbling like that, did they? I'll kill them."
Somehow, he manages to lift his arm so that his hand rests against her cheek. Her eyes widen. Very faintly, he feels the wetness of her tears against his fingers. "I don't need a reason to want to protect you, Rin. Isn't that something? I really don't...after all this time, I just did something because I wanted to do it."
"Um, Archer?"
"I'll tell you something," he whispers. Or does he speak it loudly? He's having trouble telling now. "You have the whole world, Rin. You just need to put it back together. You put me back together, so it'll be easy."
"Huh, what do you mean?" She blinks up at him. Her tears are drying up now. "You were never broken. I don't remember summoning a broken Servant, so don't tell me otherwise."
He can't feel his hand on her face any longer. He can't see anything but her. "It troubles me to ask this, but would you do one more thing for me?"
"What's that?"
"It's not such a big deal. Just smile, Rin."
"Oh." She blinks once more, and then she tries to smile. It's a weak expression, but it's enough. "I'm sorry, Archer, it's not very good."
"Jeez, don't apologize at a time like this." He smiles back at her, or thinks he does. "It's fine. You've already given me something really important, Rin."
"I haven't given you anything," she whispers. It's definitely a whisper. The tears are starting to trace their way down her cheeks again, even though she's smiling.
He leans forward to rest his forehead against hers. He can feel the warmth of it even now. "Saving you...that's one thing I don't regret. That's the only thing."
"The only thing?" She sounds surprised.
It troubles him a little how honest he's being, but he can't stop now. "You gave me a thing like that, Rin. It's really precious. I'm going to hold onto it until the world ends." His voice sounds faint. He can only feel her tears landing on his face. He can only see her smile.
"Don't go, Archer." But she doesn't use the command spell. She just keeps holding onto him.
He'll turn to dust in her arms. He'll fade away while her head rests against his. He regrets leaving her but he doesn't regret saving her, and not regretting something is the strangest sensation. "I'm really happy you summoned me, Rin."
"Then stay."
"Hah, since when am I an obedient Servant?" It's fine, because she's still smiling. "Keep smiling. I saved you so you could keep smiling. That's not so much to ask, so don't disappoint me. Rin, I-"
His voice stops working. The only thing left to him, for the next second, is his hand on her cheek. His body finally fails.
Archer sees one last thing, as his spirit trickles back to the Grail. He sees Rin nod, stand up, and wipe her tears from her face.
He wants nothing more.