Saito reached the trap door just in time to see the monsters hand breaking through the trap destroying the seal in the process. Saito readied himself that monster will destroy the village if he doesn't hold it of here, making hand signs as fast as he could.
Saito: "Water release: Water Colliding Wave."
From Saito's mouth came a huge water Torrent that dragged the Monster who just made it out, making it lose its footing and fall. The monster let out a tremendous roar filled to the brim with anger. Saito started making hand signs as fast as he could taking advantage of the fallen enemy.
Saito: "Lightning Burial: Banquet of Lightning."
The lightning traveled through the water and directly hit the monster but to Saito's surprise the monster didn't seem affected by the lightning worst it seems to absorb it.
Saito was shocked but he knew that this guy won't go down easily. He continued his assault.
Saito: "Water release: Water Jet Cutter."
Releasing a compressed line of water he tried to cut down his head but the monster managed to avoid it only getting his huge arm cut. The monster moved pretty fast considering its size.
Just as Saito was preparing to lunch another attack, he saw a shocking scene the arm he cut was regenerating at a visible speed. He knew that the only way to stop it is by delivering fatal damage to a vital area.
Saito started cursing Orochimaru and his twisted experiments. Just as he was going to preparing another attack the Monster opened its mouth. Saito dodged just in time to avoid a jet of red lightning. He kept shooting lightning while Saito activated his first phase chakra mode and started to dodge as fast as he could.
Saito started making hand signs and soon he created a water clone, before his clone is destroyed he launched an explosive tag Kunai towards the Monster. His attack landed near his leg and soon detonated. The explosion managed to stop the red lightning attack.
Saito moved in coordination with his clone closing in on the monster. While approaching he started making hand signs. And just as he reached the enemy.
Saito: "Water release: Water Prison."
Soon the water around them gathered around the monster and soon it was locked inside a huge water sphere. Even though it was a monster, it still needed air to survive. The monster started to struggle with all its power but slowly its movement became more sluggish until it finally stopped moving entirely.
Saito didn't let his guard down while his water clone maintained the water prison. Saito channeled chakra into his hands creating a huge chakra sword then with all his might he sliced the water prison in half Monster included, this move cost him almost half of his chakra reserve.
The Monster was bisected and to Saito's relief it didn't seem to regenerate.
He then took a scroll and stored the body inside. Now that the beast was destroyed he could look at the rest of the laboratory. As soon as he entered the inner chamber he saw a nauseating scene. Inside huge containers filled with green liquid animal and human bodies floated and they all suffered from horrible disfigurations. Seen this Saito could only assume that the chakra beast was the lucky survivor. Saito started closely at the test subjects they all looked lifeless. Most likely all of them died after Orochimaru abandoned this hideout. He then started to look for more documents about the experiments.
After looking through the some documents he learned that Orochimaru was trying to find a way to infuse Natural chakra into animals and normal humans. A super solider project. But apparently the test subjects couldn't handle the chakra which caused them to mutate and only a small number of test subjects survived but they ended up dying prematurely because the chakra destroyed their bodies.
After verifying that he gathered all the documents, he moved out and waited for the others to come. About half an hour later his Anbu colleagues finally made it and encircled the area.
Saito headed directly back to Konoha.
Saito was kneeling in front of the Hokage who received the full report, the Hokage was currently reading the documents. After that he took a look at the scroll containing the body.
Without saying a word he handed the scroll and documents to an Anbu standing behind the Hokage.
Hokage: "You did well on your mission. You can take a few days of rest."
Saito nodded in acknowledgement.
Saito: "Thank you Hokage sama!"
Saito will receive his pay, next time he goes to the Anbu headquarter.
Saito could only sight at the level of inhuman treatment the weak suffers in this world. Heading towards his home he heard a commotion coming from the village entrance.
There he saw Jiraya, Naruto and another two ladies. One was a blonde with a great figure and ridiculously big knockers, she was followed by a mild looking girl with black hair who was holding what looked like a pig.
Naruto and Jiraya managed to complete their mission. And the blonde should be the new hokage, he then remembered the document he saw about the sanin and now he finally saw the last one, Tsunade the greatest medical nin in the world.
Saito knew that he shouldn't let this opportunity pass by and try to get her to teach him.
Naruto saw him while passing by and started waving enthusiastically at him. Saito nodded while giving him a thumbs up.
Saito made his way back home all while thinking about how to get Tsunade to teach him.