Sarissa Theris is an asari commando with a storied military career and known for her teachings on asari honor and military tactics. She joins the Andromeda Initiative as the bodyguard of Matriarch Ishara, the asari Pathfinder.
Sarissa becomes the asari Pathfinder after leaving Matriarch Ishara to die at the hands of the kett in order to bring a kett data module containing a map of routes through the Scourge to ark Leusinia. She keeps this a secret from the other asari, knowing it would disgrace her if they learned she did not go back to help Ishara when she had the chance. The theft of the data module also causes the kett to send an elite hunter team called the Decimation, led by The Valiant, to pursue the Leusinia.
Pathfinder Ryder learns of Sarissa's actions and has the choice of keeping the secret, exposing Sarissa but allowing her to remain a Pathfinder, or exposing Sarissa and replacing her with her second, Vederia Damali.
If allowed to remain as Pathfinder, Sarissa summons a biotic shield to protect the bridge of the crashing Ark Hyperion during the battle in the Meridian sphere, saving the life of Captain Nozomi Dunn.