Thank you for the support on this, and in particular to dog1056, who left an amazing review that gave me some ideas, as well as inspiring me to write. In answer to some of your questions, the non-canon backstory will in fact be explained through Nico's dreams. Undertale's cast is almost completely dead, including Papyrus, though he may make an appearance as a ghost. Levi will not affect Nico's sword style, and finally the betrayal reason will be explained in this chapter. Others cannot be answered due to spoiler reasons.

As the horn blared out for the start of the game, shouts immediately broke out as campers charged, yelling war cries that did absolutely nothing as arrows started hurtling through the trees in response, crashing into campers without mercy. The campers wilted under the heavy fire, with only a few making it through the hail, and just a few more than that making it back to cover. Just like that, a good half the campers had been knocked out by the blunt arrows.

The attacking force went on in shambles, attempting to cover themselves with their shields, as they knew that stealth would be of little use against the Hunt. The defensive force retreated under the magical field, hoping that it would hold until they could create a counterattack. Of course, the Hecate campers saw fit to tell them then that it only would work as long as there was someone conscious under it. This was a huge problem, as the Hunt could simply make stone arrows and shoot them from outside, then just walk in and grab the flag.

With some help from Levi and Sans, Nico hatched a plan. Chiron had forbid shadow travel, as it was considered "overpowered" since Nico would be literally unbeatable. So instead, Nico summoned a skeletal deer, then had one of the two remaining Hecate campers cover it in Mist to give it the appearance of a normal deer. The deer would be able to, in theory, sneak in and grab the flag while they focused entirely on defense. The problem was that everyone else had been taken out and the hunters were right there. Fortunately, the deer had already been sent off, so they didn't see it. Nico figured they had at most two minutes before they figured out how to deal with the barrier, and then they would be in trouble. Turned out, while the other hunters went to gather stones for arrows, Thalia figured it would be a great idea to fry everyone she could. This, of course, resulted in everyone but Nico and the Hecate campers to be shocked unconscious.

With this amazing development, a barrage of arrows hit them from behind. The last campers had been knocked out, and Nico was the last man standing, literally. The Hunt circled around and came together as one group. Percy had only managed to solo about a third of them, which was pretty damn impressive, but nowhere near enough. Either that, or the others were defending, which was a scary thought, as i meant that they had lost for sure. Thankfully, the Hunt knew that they had to play aggressive, as they lacked the numbers to whittle down the camp's numbers. Therefore, it was unlikely that they had many on defense, if any at all.

The hunters were conferring, knowing they had all the time in the world, or at least most of it. One of the older ones smirked, said something, and caused the whole Hunt to giggle evilly. Nico tensed, knowing something was up, just not what it was. He would soon find out, though, of that he was certain.

The biggest hunter stepped forward, and started talking. The words streamed from her mouth like poison, hateful and full of malice, only designed to hurt. The words she was saying hurtled around in his head, bouncy balls constantly smacking into his emotions, bringing out all the hate he held for the Hunt. "Bianca's little precious," "Bianca's killer," "Bianca's brat," and other similarly crushing statements. Nico shook himself, attempting to remove the sting of the words, discovering that he had tears running down his cheeks, and the hunters laughing at him, taunting him more and more. All of them had joined in, even Thalia, and it stirred the flames of his rage. The Hunt had taken his sister, then gotten her killed. Then they hadn't even acknowledged her sacrifice, heaping all the praise on everyone else. And now, they had the sheer audacity to mock him for it?! As he fumed, Sans spoke in a dark voice,

"Let me."

Nico stepped back and allowed Sans to take control, hearing the absolute hate in his voice at these people, who would torment a young boy about his dead sister, whose death they were responsible for. His appearance started to change, with his left eye beginning to glow an eerie blue, and his right eye becoming pitch black, no pupil visible. His skin, pale to begin with, went full out bone white, and his smile stretched to larger than should've been possible, with all of his teeth showing.

The Hunt noticed the change in him, and some of them began to feel somewhat nervous, like they were doing something that would get them killed, but they shrugged it off and continued taunting him. Thalia in particular became very nervous about what was happening, and started sweating. Then. Then he started speaking, and all of them shut up. His voice was terrifying, the voice of a god, the voice of the person who decided your fate. The voice of a judge.

"So, we have some little girls who decided to try to mock me, hmmm? Well guess what. Today, I'm going to show you what happens to a little dog who barks too much at a bigger dog." Sans' voice echoed around the forest, dark and terrifying.

The Hunt started laughing. Doesn't matter how scary your voice is, in the end it's one against a good twenty. Then they all got lifted into the air at once, and they stopped laughing. Then got thrown into trees. Then odd, draconic skulls appeared around each of them. At the end, they were looking at him with fear, which doubled when the skulls opened their maws and light began gathering in each of them.

The big hunter, Nico remembered her name to be Phoebe, tried to pull a bow, but then the skull unleashed its blast, and within the span of half a second, blew her bow to pieces. The skull already had another blast ready by the time she registered what happened. Bones flew up from the ground, and encircled her, ready to stab her if she tried anything else. However, something caught their attention, which was the deer sprinting back with their flag firmly in its teeth. The deer walked over to Nico, dipped its head, and proffered the flag to him. He took it, and smirking, placed it with his own flag, whereupon it turned to pitch black with the helm of darkness on it(In this CTF, you must put the opponent's flag with yours, to make it a more difficult game). He walked back to them, sighing, then said to the deer,

"Isn't is sad the way that assholes never win? Oh true, I guess I'm wrong, they do win quite a lot, but only if they have powerful friends. Such a shame that i don't give a shit about said friends."

Nico laughed crazily, as Sans retreated back into his mind, due to the massive power rush he was experiencing right then.

However, he turned around at the sound of a cough, and saw the entire council, with Apollo and Hermes giving him discreet smiles and thumbs up, Hades looking rather proud, Ares and Aphrodite struggling to keep from laughing at the situation the Hunt was in, and Artemis along with everyone looking absolutely furious.

Nico looked at them all, smirked, bowed, and said smugly, "There's one for Camp Half-Blood."

That's the end of this chapter. Please do review, as it is quite nice to have input from other people about which way the story could go. Again, thank you to dog1056 for the amazing review, and have a good time!

P.S. I am a fan of Good!Chara and Evil!Frisk, so, fair warning.