
When Isaac realizes he has been hearing Nicole's voice and seeing Nicole, he leaves Aegis VII. But on the shuttle, Isaac is acting very differently, implying that Isaac has been affected by the Marker in ways other than just being reminded of his deceased ex-girlfriend.
In the original conclusion of Dead Space 2023, Isaac vanquishes the Hive Mind and returns to his ship. However, as he is running away, he appears to be attacked by a mutant Nicole in one of the greatest jump scares in video game history. Shortly after, the game transitions to the credits. In the alternate ending, after gathering all the Marker fragments, Isaac Clarke fully succumbs to a mental breakdown. When he leaves Aegis VII at the end of the game, giving in to his hallucinations of Nicole, and returns to Earth, he then fully submits to the Dead Space Marker itself. Dead Space's new ending is a complete remake of the original work by developer EA Motive.
The implication, according to reports, is that Isaac accepts responsibility for returning the Marker to Earth and releasing the necromorphs there. That undoubtedly cannot be good for anyone, including our brave protagonist and the entire human race. In addition to making up for the fact that Dead Space veterans are aware of the impending jump scare in the original ending, as others have noted, this conclusion also fills in some previous logical holes.
After all, there's a good chance that the original Dead Space development team had no idea that they would have the opportunity to create a sequel or even what they would do with it. This covert ending appears to confirm that the developers of the Dead Space remake intended to respect the lore of the second game and wanted to make a more direct connection between the two games.
How to unlock the secret ending in Dead Space 2023?
For the secret ending, you must collect all 12 Marker fragments. The secret ending is unfortunately not accessible on the first playthrough, despite how simple that may sound. The designers of the game purposefully created it so that you must play through it a second time in order to unlock it. Fortunately, you can play on any difficulty to get this ending; there are no restrictions on it. So, here's how you can quickly discover the secret ending:
Finish the game in Easy mode. Easy is recommended for completing the game quickly; the difficulty has no bearing on obtaining the secret ending.
Start a New Game+ and select any difficulty level you want, but play on easy to get to the end faster.
Keep an eye out for purple glowing orbs in any area you're in while playing; these are Marker Fragments, and they're fairly easy to spot.
Simply continue the game's story after you've collected all 12 of them.
When you complete the game this time, you will receive a different cutscene as the secret ending.

What is the plot of Dead Space 2023 in brief?
The Kellion crew arrives at the outskirts of Aegis VII, but due to a docking error, they crash land on the Ishimura. Isaac, Kendra, Hammond, and Chen investigate the allegedly deserted ship while a hurt Johnston stays behind. The team is forced to split up when Necromorphs made from the corpses of Ishimura's crew attack and kill Chen.
While fighting the undead crew, the team investigates the Ishimura to repair its damage and learn what caused the outbreak. While a reanimated Chen is subdued by Hammond and ejected from the ship, Kellion is destroyed by necromorphs, killing Johnston.
While on board, he discovers the presence of the fanatical Church of Unitology and its leader, Mercer, who aims to bring the Marker to Earth. Isaac is hostile towards Unitology as his parents were killed by a murder-suicide orchestrated by his mother, a devout Unitologist.

Isaac and Nicole sabotage Kendra's plan to bring the Marker back on Earth, causing Aegis VII to collapse. Kyne is shot dead by Kendra, who reveals she is allied with the Earth Government. Isaac finds Mercer and a captive Temple with the man-made Marker, and Mercer flees after murdering Temple before he is killed by Necromorphs.
Nicole committed suicide in order to avoid being reanimated, and Kendra finds the Marker and tells Isaac that Nicole has actually been dead the entire time. He was actually with Cross, who mistook Isaac for Temple while the Marker controlled the two to send the Marker back to the planet's sizable Necromorph Hive Mind. Aegis VII and the Marker are destroyed as Isaac kills the Hive Mind and barely makes it out alive. Isaac is attacked by a hallucination of Nicole while he is sleeping.
What is the setting of Dead Space 2023's plot?
The story takes place in the 26th century and centers on engineer Isaac Clarke, a crew member on the USS Kellion, a repair ship sent to the USG Ishimura, a sizable planetary mining ship that has stopped operating above the planet Aegis VII. Kendra Daniels, a computer specialist; Zach Hammond, a chief security officer; and Cpls. Hailey Johnston and Aiden Chen, co-pilots and security personnel, make up his crew.

The crew of the ship is attacked by Necromorphs while they are looking into a distress call sent by Nicole Brennan, Isaac's girlfriend, and the ship's medical officer. Isaac is left to fend for himself as he works to save the crew members he still has and learn the truth about the sinking of the Ishimura.