I'm fairly sure this has been done before, but if it hasn't then here we go!
Disclaimer: I'm not Rick, nor will I ever claim to be.

Pity

He pitied her.

That was it. He didn't love his own daughter enough to save her life -- or allow her a human body, at the very least.

He watched over his shoulder as her legs and body and head became encased in a woody trunk, as her arms sprang out, stiff as boards, and were covered in bark. He saw the needles growing, fast as lightning, green and fresh and new and plant-like.

He sulked for days, and those days stretched themselves into weeks, and those weeks stretched themselves into months, and every single day he went to the pine tree and prayed to his father and aunts and uncles and every god that existed that she could hear him somewhere. The pine tree saved his life more than once, and in more ways than one, and it was the one thing he missed the most.

But then the dark part of his mind awakened, and he looked for people to pin it on. The first was, most predictably, he himself. If he had never struggled against the satyr, they would have gotten there sooner. If he had never fallen for the Cyclops's trick, they wouldn't have caught up.

Next was the satyr: It was him who took some wrong turns and into the Cyclops's lair. It was him who forced them to come to the wretched camp, where he was immediately crammed in with twenty other boys and girls just like him. It was him who persuaded him to leave her and save himself.

But that wasn't fair, was it? Hadn't he agreed, however reluctant? Hadn't he let himself be swayed away from her, and let her make her final stand on her own?

It all came back to him again. Some call it survivor's guilt, but he called it a broken heart; a powerful ache inside his very soul that could never be repaired, a hole shaped exactly like her and her punk clothes that could never be filled by anyone else.

Then he picked her: the little one they had helped out of an alleyway, who was using a mallet as a weapon and had no idea how to survive. It would have been easier; she had been a powerful half-blood, and they knew it, because the three of them seemed to attract even more monsters after she joined them. They could have moved faster, got there quicker, in time. . . . After giving her the cold shoulder for a few days -- which she didn't understand -- he'd found another person to blame.

Himself. Again. Wasn't he the one who suggested he take her with them? He could barely rembember now. It seemed that was a different life: one with her in it, and one without. But if it was her, than he was the one who approved. It was his fault they were slowed down.

Then he blamed her for her own death. After getting past the harpies at night, he'd scream at the pine tree utterly ridiculous reasons. "Why did you have to be so noble?" "You could have made it!" "I wish I'd never met you in the first place!" The insults would get worse and worse, and when he finally said, "This is all your fault!" he broke down. It pierced him, another little piece of him dying: the good piece.

He would fall down to his knees, a tear or two -- or three or four or five -- dripping off his nose or his chin. And then he would say in a hollow voice that didn't belong to him, "It's not your fault." Every time he would come close to saying something else, but it never got past the lump in his throat.

Then he would attack himself again, refusing meals and skipping all the activities and training -- all except sword fighting. He slashed and hacked at the stuffed dummies, straw flying out in giant bursts, sweating enough to fill nine buckets. He'd duel the other campers with, it seemed, extra strength, leaving them to walk out of the arena bruised and battered.

Finally, finally, after years of pointless accusations, he found one person -- or group of people -- and stuck with it: the gods. Zeus was the one who failed to save her human life, and instead turned her into a tree. Hades was the one who sent all of his monsters after her, all but forcing her to sacrifice herself.

So he turned himself over to Kronos. He befriended the Son of Poseidon, and, unfortunately, failed to kill him.

Then he had to poison her tree.

It had taken all his strength and willpower to do it. A few traitorous -- much like himself -- tears had fallen, but not like those nights of blaming and yelling; they had to disappear, and he made them disappear. For the whole time, he forced himself to think of the gods and only of the gods. Just before he left, he stopped and looked at the tree that used to be -- and would hopefully be again -- the girl that broke his heart. "I'm sorry," he whispered before sprinting into the darkness.

With much persuasion, he went the River Styx. He felt himself slipping away, his soul being torn away like so many others, until she somehow wormed her way back into his counscious memory. "Come on," she said fiercely from above him, spear ready like he had seen before. "Get off your butt and fight, I can't tackle all these on my own." She held out her hand, and he took it.

He battled her on Mount Tam, and yet another part of him died. He saw how much she wanted to switch sides just because he was there, but it was so plain how much betrayal she felt and how little she now trusted him. He felt her semi-final blow knock him off the cliff, felt the crash that should have shattered his bones.

But that pain was only coupled with another pain, a new one, a pain that assumed its old place when she joined the Hunters and turned her back on him forever: His heart broke all over again, because now, if he ever got a second chance, it was far too late.

Now he lay dying on the floor of the Olympians' throne room, looking into the face of the sixteen year old he'd met nearly ten years ago in an alley.

He contemplated the sentence that had come from his mouth; he had to know. He just couldn't leave her hanging like this. He saw her glance at him, and he would have smiled if he hadn't twisted himself and put himself through all this pain.

He sighed in relief; that was what he'd hoped. He tried to tell her with his now-regular-blue eyes to pass on a message, and something in her gray pair seemed to flicker in understanding. He turned to the boy.

He clutched his shirt sleeve, hoping to make the message all the more urgent. He watched as the hero of Olympus nodded and made his promise, as they both apologized with no words. He wished she were there, but she wasn't, and he would have to work with what he had.

He saw the Underworld, the opposite of the stone city above the clouds, begin to come into focus. He understood now what Zeus was feeling, because he knew how it felt; he went through it for years, and now she had to live with it for eternity.

Luke Castellan pitied Thalia Grace.