After Tatsumi also known as Master Chief was transported into a new world. He got a new memories of Training (Marksman, Hand-to-Hand Combat, Close Quarters Combat, & Leadership), Augmentation, Joining UNSC (United Nations Space Command),

and His Allies and Finally Going into the War against Alien Threat called The Covenant. Master Chief and his new team: Blue Team was assigned to rescue the Cadets in Corbulo Academy. As Covenant Elite was about to kill them when Master Chief kills it with his combat knife then walks up to them.

Master Chief: We don't have much time, let's go.

Then after the cadets were equipped with their armory, He escorted them to safety into extraction point.

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They took a warthog as one of the cadets named Thomas Lasky drives it. Master Chief fires his machine gun turret neutralizing the Covenant Troopers.

Master Chief: Kelly, Set coordinates of evac.
Cadet: I think we're cleared.

Then they stopped due to Warthog's damages they set on foot then they were ambushed by the Hunters they took the cover as Hunters searches for them.

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After Lasky is fully recovered they made it to the extraction.

Kelly: Alright. Get in.

They made it to the pelican as they were about to take off.

Blue Team successfully rescued the cadets. Master Chief gave some sort of fragment to Lasky.

Master Chief: Well done, soldier.

Lasky was surprised that He impressed him and Lasky became inspired by the heroism and the leadership of the young Spartan super-soldier.

Then Years has passed. The Fall of Reach where he and other Spartans trained affected John and he has some companion AI named Cortana then they came to a battle on Earth next is the Installation of the Halo Ring. Cortana activated the Halo Ring and Master Chief and Cortana made it on board the Frigate: UNSC Forward Unto Dawn.

But due to Slipspace Stress. The Dawn split into two one at front crashed into the Earth while the second lost in space.

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He won every battle but the war is far from over. As the Dawn was heading towards the Unknown planet.