Isaias is first seen in his debut appearance in the Sarif Industries headquarters ib Detroit where he is with William Taggart as he speaks to David Sarif. Adam Jensen walks in after he returns from the FEMA Camp Facility in Highland Park. Jensen confronts him and Isaias reveals his deep hatred for human augmentations from past experiences where he had helped dozens of people in the past dealing from neuropozyn addiction and implant rejection where he saw the worst effects of both cases. He then reveals that he has a brother who was an augmented veteran and was given military augmentations but went on a rampage in a shopping mall where Taggart talked him out of it and preented any deaths. Since then, Isaias has had a personal debt and loyalty towards Taggart.
Later on when Jensen is in the Picus TV HQ in Motreal, Canada, Eliza Cassan reveals to him that Isaias was personally involved in the attack on Sarif Industries where in a hologram message, he is seen talking to Jaron Namir on how he must remove implant chips of Megan Reed and her team in an effort to keep them alive and hidden from the public eye and get kidnapped easier. Furious at this report, Jensen returns to Detroit to confront Taggart as Humanity Front activists and members riot outside and ravage the city and eventually Jensen finds out where Isaias is and heads towards the run-down apartment that he's hiding in. Jensen heads there and finds the place to be overrun with Purity First members and it turns out that Isaias was a member of the organizationa dn secretly supplied them from behind Taggart's back due to his distain for violence.
Once Jensen finally confronts Isaias, he is seen at a TV and is angered over a report on it. He tells Jensen to stay away and threatens to kill himself if he doesn't comply. Isaias then begins to have a semi-breakdown and claims that he's a mass murderer for his assistnace of the Tyrants in their operations. The player can then choose what direction to take the conversation. If the player chooses correctly, Isaias will live and will tell Jensen that Megan is alive and where her team is at but if the player chooses wrong, he'll kill himself. If kept alive, Isaias gets arrested afterwards on charges of terrorism.
Isaias appears to be an average hispanic male in his 40s. He has dark skin, black hair, and a small mustache. he wears a black suit with a red and dark brown/redish stripped tie.
Isaias has a depp hatred for augmentations stemming from past experience and cases where he delt with the worst of augmentation rejections and neuropozyn addictions and thus wants them heavily regulated if not banned in general. He's very loyal towards Taggart for helping his borther Exekiel get out of killing people in a mall and thus is always by his side and tries to please him. Isaias is also very insecure and irrational as he can fall into a gloomy/depressing mood veyr easily and seems to be easily agitated as well.
- If Isaias commits suicide and the player picks up his weapon, it'll have five rounds despite only one bullet visibly being loaded into it.
- Both Isaias and Exekiel are the names of prophets in Christianity and Judaism.
- He has an Omega Type personality.