Blaise Madeline Corso was a detective of the San Francisco Police Department, and was serving as the tritagonist of the game. As of V16C6, she is currently imprisoned at life sentencing for the murder of Kolo Zargoza. And, as of V16C7, she died to protect the city of San Francisco from Dr. Mensra's Nightmare drug.
Blaise was originally from Bakersfield, California. She grew up in a trailer. Her father abandoned the family when she was 4 years old. Her comment in a Volume 11 bonus scene to her mother (whom she seemingly is in regular contact with) Madeline Corso is that she is her youngest daughter; this means she must have at least one sister.
She first transferred in from Bakersfield and was immediately assigned as Mal Fallon's partner. Their first case was on some gangland murders in the area. The two didn't attend college together, however Blaise has heard of his college rock band.
After leaving for an anti-terrorism joint task force, she then returned to the SFPD at the end of Final Flight (V7C8). In her second appearance in Tendrils (V8C1), she aids Natara Williams in a bank robbery case in a reckless manner, something of which Natara does not approve.
In Volume 8: The Kraken, Blaise worked with her Mal a lot more than Natara since Natara was kept in the dark on the situation due to the Kraken being Shawn Mallory. She rebelled against all moral ethics and, out of anger about the murder of Ken Greene, kicked Kolo Zargoza off a roof, killing him even though he had already fully surrendered to Corso. She kept this a secret from everyone until she had told her psychiatrist in Volume 15 and . Jeremy Redbird in Volume 16. In Volume 9: Livewire, Blaise is being watched closely by Internal Affairs due to her rebellious nature. She is often partnered up with rookie Jeremy Redbird so he could enforce the rules on her. However, Blaise gets away from the precinct when Mal needs help rescuing his father, Jacob, in Las Vegas. She impersonates Bardan Stone's favorite cocktail waitress, Fiona Flynn, and accompanies Mal in the poker tournament he is to enter to win the money needed to free his father from the clutches of the Flores cartel. While in Las Vegas, Blaise attempts to seduce Mal and reveals that she has feelings for him. After Mal turns her down, she suggests he go after Natara, which he eventually does. Blaise is still loyal to Mal as a friend and helps him through a lot. However, since she was injured from the cannibal killer, she could not join the task force to save him in Volume 11.
After being paired together on a stressful terrorism case, she started a "purely sexual" affair with her best friend and partner Jeremy Redbird. She later develops more feelings for him and struggles with how to deal with them. Blaise appeared to become emotionally unstable (and confided in Natara) in V13C6, shortly after Jeremy was stabbed in the chest by The Ghost. In V14C1's bonus scene, she broke up with Jeremy, and in the following episode, she became Mal's work partner after Natara joined the SCT. In V14C3's bonus scene, she meets the psychiatrist who was counselling Jeremy and tells him that she needs help. She appears to have recovered from the psychological impact of her breakup, and (quickly) made up with Jeremy in V14C6. In V14C9, the pressure from almost being killed by the same man who almost killed her a few years ago (as first flashbacked in the bonus scene of the second part of the side story Peacemaker), Firstborn, caused her to tell a psychiatrist (in the bonus scene) that she did execute Kolo Zargoza. She also says she doesn't deserve to put her badge on because she's a killer, no better than the other killers who she hunted down in the past.
She initially turned down Captain Maria Yeong's offer to join the Special Crimes Task Force to pursue the Firstborn due to personal reasons. It was later revealed that the main reason that she didn't want to join was due to the fact that she was afraid of being near her ex-partner, Jeremy Redbird as she was unsure of her feelings towards him. However, she soon decided to join the SCT as she started to find being alone without her team boring. She was once again given the opportunity to join the SCT and accepted the offer. She was shown to have join the team in the side story, Holiday Stories: Past & Presents.
In Tokyo with the SCT, Blaise Corso and Jeremy Redbird are investigating the home of the Orgo. A bomb deactivated exploding the house containing both Detectives inside. She survives but believes Jeremy Redbird is dead. She hunts down the Firstborn where she finds him and asks him why she was so important to his plan for all these years. The Firstborn however, does not remember her and says she truly meant nothing, it was trick he had pulled on her. The Firstborn had escaped.
Returning to San Franscico with the SCT, Blaise goes home but is seen to be having nightmares about the murder of Kolo, Jeremy Redbird comes to her home and has a talk about her options and how she is feeling. The next morning she hands in her gun and badge telling Lt. Charles Anders that she should be arrested for the murder of Kolo. She was to be sentenced to life.
In V16C7, while the SCT was squaring off with The Firstborn for the last time, Blaise hitched a ride in a helicopter carrying enough of the Nightmare drug to coat all of San Francisco. She blew herself up far enough away from the city that the inhabitants were safe, despite Anders and Amy telling her not to. She dies a heroine, and a martyr. And,
"You know what? I don't think she was scared, at all."
- It was revealed in the bonus scene of Truth or Dare, Part 2 (V10C3) that Blaise had dyed her hair green and had piercings but had to remove them out due to her joining her high school's wrestling team. She was kicked off the team from punching too many people.
- In the Fourth of July Special, it was revealed that she used to be part of the Joint Terror Task Force with Greg Washburne of Homeland Security and went under the false name 'Irene Rialo'.
- 13-1 reveals that Blaise has an intense case of arachnophobia, however she denies this and just claims that she wants to kill every spider she sees.
- At the end of the Series Finale bonus scene, Natara reveals to Mal that she is pregnant, and they decide to name their child after Blaise, since it is a unisex name.