Son of Tartarus

Unluckily, I learn to use my powers

As soon as Tina pressed the button, we were down in the Underworld.
"We did it" Jay said
-"Yes!" I exclaimed
  The nearer we got to Tartarus, the better it got for me and my powers. Today was July 3. We still had 28 days to be able to do this in time. It was almost Impossible for us to fail. We had fallen in nearby a big palace, but we knew we were in the Underworld because Thanatos' iPad instead of having the time, it said "Underworld Times are Complex". Harry put Thanatos' iPad back in the bag and it disappeared.
"Is that the palace of Hades?" I asked
-"Yes, but be careful, the palace of Hades is right next to the entrance to Tartarus, so your powers might be stronger here, but the chances of getting attacked are bigger" Shaggy said
As if on purpose, when he finished a big monster stood on his back. It had the head of a lion, the body of a goat, a mane, and a long black snake-headed tail which grew out of its back. A chimera.
I took Shade out, and so did Tina, Jay and Harry with Kypello, Sitari, and Titan Slayer. Shaggy took his pan pipes. I was going to attack, but when I got closer, the beast jumped above my head and aimed for Jay. He fell to the ground. Next, Tina used Kypello to cut through its neck, but the chimera grabbed her with its tail and the snake had her. Harry ran around it slicing through until it put a paw in front of him and he slipped over. The snake took Shaggy's pan's pipes. All of this happened at the same time. I ran towards it with my sword in his direction, and when I sliced through a bit, a big hole opened in the ground. It was really deep. The monster fell into it, and unluckily, so did my friends so I had to follow.

...

While I was falling I tried to remember what I knew about Tartarus, but falling deep while fighting a monster who is trying to kill you and your friends is not that easy. Yeah, the chimera fell with us.
Shaggy, Tina and I were the only ones awake. Harry and Jay were quite fainted. Shaggy got his pipes back when Tina cut the monster's tail. I hurt him pretty bad with Shade. The chimera was fast though, and it attacked quite a lot too. I was doing fine (well, as much fine as you can be when you are flying and fighting at the same time) until it got me with its paw and used it cut my skin. Shaggy was playing a song, but I didn't know what it was supposed to do because we all seemed very good and awake, except of course for Jay and Harry. Suddenly, I had a terrible idea, so of course I used it.
  I grabbed Hermes's bag and opened it as wide as it could go. Then, I grabbed Jay and Harry and got them inside the bag. Stupid.
  I turned back to the chimera just in time so that it could hit me in the face. I sliced through his body, taking the kill. The chimera disappeared.
  Tina, Shaggy and I were scared, and tired, but we stayed awake as long as we could. Shaggy played a song for that.

...

  It took days, I am sure of that, but at last, I saw the ground. Tina was asleep. I woke her up. The ground was black and very far away, but it was visible. Then, I realised there was a river in the ground. I aimed there. Tina and Shaggy seemed to follow. I looked towards the water and remembered the stories about the five rivers of the Underworld: The Cocytus, the Phlegethon, the Acheron, the Lethe and the Styx. How could I forget the Styx? This entire mission was all about that river.
I grabbed Tina's arm and pointed to the bag. She understood, although she was clearly very scared. She entered. I turned to Shaggy, unluckily, he didn't understand. I grabbed his arm, but he pulled himself away. Then I fell.
The water was so hot I felt like I was melting away. Do you know when the wax in a candle melts and it falls to your finger making you feel the ultimate pain for a second? It felt like that but it was not just for a second, and about ten times worse. The Phlegethon. Fire water. It was horrible. Shaggy was swirling in pain. I felt like it would have been better to die, but still I didn't. I swam as fast as I could which was really slow to the glassy shore. I took a breath. It was hard, probably the hardest thing I had ever done. I opened the bag and reached for Tina. She was there, so I pulled her. She was okay. Then, I fainted.

...

I woke up later, to find everyone in the shore. Even Jay and Harry who I hadn't seen in days. Shaggy was fainted as well, and he looked horrible. His clothes were quite tattered, he was bleeding and his face was half burnt. Then I realised I probably looked like that too.
"Finally!" Harry said
-"Are you okay?" Tina asked; She sounded genuinely concerned.
-"Yes. Sort of," I said
-"Look, it is already July 13. Ten days. Ten days since we started falling." Jay said while showing me a calendar that they probably took from the bag.
-"Impossible" I said
-"Well, you were like that for a day." Tina said
-"What? And the other 9?" I asked
-"The fall probably" Jay said
-"No way" I said
Jay took a deep breath. Then he spoke.
"Looks like it"
-"Well, if it takes 9 days to come here, I bet another 9 to go back. Today is July 13, so, 9 days to come out assuming we start today, so it would be July 22. That would leave us only 11 days." I calculated.
-"Yes, but we can't leave today. The Styx is somewhere here in Tartarus right? We must find it first, or we will run out of time." Tina informed.
-"Can you get any help from your father?" Jay asked
-"I dunno. Let me try." I said.
I kneeled down and put my hands on the ground. I kept like that. I could feel the power running through me. Suddenly, I felt my soul leaving my body. I was above me, if I looked down. But that wasn't just it. I could see any direction and see miles away in that specific direction. I saw monsters, darkness, at some point, I saw Annabeth, the same girl I saw on my first nightmare, but she wasn't alone. She was with two guys. One seemed like a regular teen, and the other one was a big humanoid about who knows what feet tall. I hoped they were okay. Looking deeper in that direction I saw, first a black shrine with a caduceus, Hermes' probably, deeper I saw a house made of bones, deeper I saw a black mansion, like really black, and lastly I saw an army of monsters blocking the way deeper to Tartarus. I decided we should not go that way.
Looking on another direction, I saw a cave, a humanoid monster which I didn't recognise, deeper I saw a river with black water and next to it, two things: a monster which was big and dark, and a book that read: 'BIG BOOK OF PROMISES'. Promises. It was the Styx.
I lifted my hands of the ground and my spirit came back to my body. I turned towards the direction I saw.
"That way" I pointed.