STREGAStrega is a secondary antagonist group formed in Persona 3. They use the Dark Hour for their own personal benefits. The group includes three Persona users, Takaya Sakai, Jin Shirato, and Chidori Yoshino. Takaya, the leader, as well as the other two, set up an online website called "Revenge Request," where they take personal requests to assassinate people in the Dark Hour. The members of Strega are artificial Persona users created by the Kirijo Group, who picked the three members of Strega off of the streets, using them for their experiments. Due to the fact that their Personas were not naturally awakened, they must take suppressants that are supplied by a man named Shuji Ikutsuki. These drugs prevent their deaths from their Personas, but they have very lethal side-effects.
Takaya leads the group to assassinate helpless victims in the Dark Hour. Jin usually acts tough, but he is still just a follower. In a scene in Persona 3, a helpless teenage boy is shot by Takaya. Chidori is seen looking away during this process, and only talking when she tells Takaya that he isn't dead yet. Takaya doesn't even take mercy on the pain the boy is feeling, leaving him there to suffer or to wait until a Shadow kills him. Chidori clearly does not enjoy being apart of Strega, but she follows them around because she simply has nowhere else to go to feel accepted. The three are all in the same situation with the same fate, and therefore stick together.
Strega clashes with the main group, S.E.E.S, because of their different opinions on what should happen to the Dark Hour. Takaya, being the most manipulative character in the game, tampers with Chidori's thoughts, making her think of Junpei and the other members of S.E.E.S as a nuisance, and evil, for going against their main ideals. Chidori starts seeing Junpei in the town, and presumably once Strega finds out, they force Chidori to use him in attempt to end S.E.E.S' battles. Once S.E.E.S defeats the boss battle, they save Junpei and capture Chidori. Pissed, a few months later, Takaya and Jin show up in the hospital to "save" Chidori. I put save in quotations because once they get there, they have "tools" to take her by force if needed. They show up with rope and bondage, things that they can forcefully remove Chidori from the hospital if they must. However, she willingly follows them once they tell her she doesn't have anywhere or anyone to go to.
In the final battle between Chidori and S.E.E.S, S.E.E.S wins. Junpei runs over to her and tells her not to follow Strega anymore and that she'll be accepted if she comes with him. Once Takaya and Jin show up, they tell Junpei he has poisoned Chidori. When Junpei tries to stick up for her, Takaya shoots Junpei, killing him. Chidori gives her life to save Junpei. After she dies, Takaya announces that her life was wasted and pitiful. Junpei gets pissed off and tries to fight them, but they end up leaving. Chidori wasn't respected by Takaya or Jin, and in the end, they called her useless. Junpei and the rest of S.E.E.S cared for her and sincerely wanted to protect her. This is the exact opposite of her own group, Strega, who just accepted her because they were all forced into the same circumstances.