Sinon is the personal assassin and pilot for Commander Heathcliff.
Sinon met Commander Heathcliff for a covert op for an unknown reason or purpose. Since then, the have been in almost every battle together, while she has also killed targets he was unable to get to for various reasons. Sinon uses an extremely precise weapon of which there are very few. Sinon usually helps Commander Heathcliff with getting around, considering she is the pilot of the two of them, and also protects him from harm even he does not know about.
On one mission, Sinon was brutally hurt when she had decided to take on a contract without Commander Heathcliff, although he also thought it was going to be fine. Her and five others, making a team of six, were to ambush and kill a small Chat Nation group, as they had been doing for about a week to the groups attempting to get to the location where they needed to retrieve some resources. Sinon took the first shot, and killed one of them, while her teammates killed another of the enemy group. however, there was a cloaked enemy and when he removed his cloak, Sinon and her team found out he was carrying a minigun with him. This minigun user then proceeded to pin down and kill two of Sinon's teammates, and she decided she needed to do something. She went to her teammates who were left, and asked them to give her cover so she could kill the minigun user. As they did so, two more of them died, but only the minigun user and another were left. she went into a building, but the minigun user had predicted her to do so, and pointed to where Sinon was heading. As she realized this, she decided to jump out the window, although her left leg below the knee was gun due to the minigun. As she was above the minigun iser, she fired her sniper rifle and killed him. Sinon radioed for help and the dropship that was to take their team of six home ended up taking a wounded Sinon, and the only other survivor of her team home.
Since then, she has never gone on a mission without Commander Heathcliff, and tries to remain more aware of unexpected possibilities.
Sinon has blue swaying hair that is casually short, but has tufts of hair tied up on both sides of her face, and indigo eyes. Sinon is approximately 161 centimeters tall and is in her early twenties. Sinon always carries with her her prized sniper rifle, the PGM Hecate II, around with her at all times. It has been specially modified to be able to shoot around 2,000 meters by the average sniper, although Sinon is somehow able to use it effectively up to 3,800 meters. The weapon is at least 13.8 kilograms, however it usually weighs much more than that. The PGM Hecate II is 138 centimeters long and uses .50 BMG ammunition, which Sinon has to make herself. While it was originally designed to be used against vehicles, Sinon makes use of it as an anti-personnel weapon, much to the chagrin of her targets.
Sinon's left leg below the knee is a prosthesis of an extremely advanced nature and is colored the same color as her hair. When she is in combat, her attire is a desert colored military jacket, bulletproof armor, and combat boots of the same color, and a white scarf around her neck.
Sinon is almost always extremely calm and stoic, much like Commander Heathcliff. Although she is usually like this, she is not devoid of a sense of humor, being one of the few people that can make Commander Heathcliff laugh. While it is unknown what Commander Heathcliff and her are planning, it is known that is they are not fans of the Chat Empire. While some have questioned why she has blinding loyalty to Commander Heathcliff, only Commander Heathcliff and her knew.
After Sinon and Commander Heathcliff survived The Ambush at Gaeto, she fought with Jess about what to do, whether to chase after Hatsune Miku, or wait for the soldiers to heal. After Commander Heathcliff awakened, she was proven partially correct, as they were leaving, but not to Hatunse Miku, they were going to attack Eafth.
This entailed quite a job for Sinon, considering she was the pilot of The Hecate . She accepted this as a challenge, and prepared the ship for the plan. She had quite the time following Commander Heathcliff's orders, but did all she was able to do, unfortunately, The Hecate was heavily damaged in the process.
After they escaped from the SOLEL system, DMR4LIFE attempted to leave, and in emotional distruaght, hit Sinon, who quickly retaliated by bringing a knife to his throat, although he got her off of him. After which she made sure no leaks were currently in the hull of the ship. After they arrived to the repair station, she reunited with her daughter, Andare, and it was revealed that her and Commander Heathcliff were together and had Andare almost 23 years ago. The reason Andare and Sinon look so similar in age was also explained to DMR4LIFE, Forerunner, and Vidmas7er. The reason Sinon appears so young is because she has spent many years in cryostorage, only coming out of it after Commander Heathcliff felt she had been in there for too long, there was a mission, or she felt like not being in the cryotube. Her real age is similar to Commander Heathcliff, which would make her chronologically older than 60 years old, although her physical age is less than thirty.
After the battle on Catoonie, in which Commander Heathcliff was severely injured, she was truly worried for him. She also told Vidmas7er and Forerunner that she has had it easier than Commander Heathcliff, since she has been in suspended animation for over 40 years worth of time, compared to him, who has been alive this entire time, in order to see a time for an opportunity to get Hatsune Miku back.
Sinon would next see combat during the opening phases of The Chat Schism. Helping Heathcliff and her daughter, Andare, the team was part of an all out assault on Eafth. Their mission was to rescue the AI Blue from KnightmareS-C075. While Heathcliff was busy fighting Bravadostock, the two girls got bogged down fighting another Miku bot and a fireteam of Chat Bodyguards. While Blue was ultimately saved, it was by the hands of Jess McKathy and Karl-591. She would next see action attacking a Chat base deep in the mountains, with the intent of freeing Vid from the Chat. The mission was a success, with Vidmas7er being safely brought aboard the Hecate. The team then made their way towards Gaeto for a delegation.
While Sinon spent most of the delegation aboard the Hecate, she was aware of the events going on. While the disappearance of Jess, Sinon is now apart of a collaborative effect to bring her back safely.