I’ve been wanting to get a Psi character added to the roster for a while, and OW2 gives me an idea for how this character could be introduced as a newbie to Overwatch.
In Canada, Overwatch learns that an entire town of people has somehow lost consciousness all at once, all except for the local Omnics and one girl named Caitlyn. Sojourn reveals that she knows this girl, and that she is a potent psionic (a trait that only appears in about 1 in every 500,000,000 people). Sojourn had been keeping tabs on her, so she contacts Caitlyn and learns the girl had released an uncontrolled psionic shockwave during a moment of intense stress. Sojourn suggests that Overwatch go and retrieve Caitlyn, as she could be a danger to others if her powers go rampant. Unfortunately, as Overwatch is flying to her, Caitlyn sees several Talon dropships flying overhead toward her town. Realizing that Talon is aware of Caitlyn’s existence and that they want to turn Caitlyn into a living weapon like Widowmaker, Sojourn tells Caitlyn to find a place to hide until Overwatch can get to her.
When Overwatch arrives at the town, their transport is hit by a Talon thug wielding what would basically be an M92 Stinger equivalent, causing their dropship to crash land. Overwatch blasts their way out of the crash site and engages Talon’s forces while doing whatever is needed to avoid civilian casualties. During the battle, Sojourn keeps contact with Caitlyn to try and keep her calm, as she doesn’t want Caitlyn releasing another psionic wave during a battle. But during the fighting, Talon is able to tap their communication (Sojourn was expecting this, but didn’t think it would happen so soon), and they use this to locate Caitlyn. Overwatch rushes to Caitlyn’s hiding place and arrive just in time.
Caitlyn is caught in a crossfire between Overwatch and Talon, and the stress causes her to nearly release an even more powerful psionic wave, one that could end up killing everyone around her. Sojourn is forced to shoot Caitlyn with a tranquilizer to knock her out. The remaining Talon forces are arrested, having been incapacitated by Caitlyn’s Psi wave. Caitlyn then goes with Overwatch for protection, while Winston and Mercy try to come up with a way for Caitlyn to control her powers.
Later on, after Winston and Mercy successfully develop technology that allows Caitlyn to better control her powers, she offers to join Overwatch. Cue a combat training montage ala Symphogear.
Having her join after the mission as a total newbie would help keep her from being overpowered, both in-game and in-universe.