My best shot at the Dareka plot: (only discovered it this past week)
Rena meets a guy
??? (elaborate later)
Rena now poor, feeding sick someone.
Rena ends up in crime/prostitution
Rena sells out her friends to pimp
Friends get kidnapped a la Taken
Shot of them lying down asleep/dead, which is symbolic of Rena having killed them because now they'll be forced into prostitution
Seifuku ga Jama wo Suru!
Sawako either resisted or disobeyed during the job, so is punished.
Deguchi has successfully integrated into whoredom so is not punished. She'll probably become the next Rena.
Rena cuts her hair out of guilt.
That's the general storyline. Other bits can fit in different places and still fit, hence the ??? section.
Either the guy dumping her could have driven her into crime or the guy could have dumped her after the kidnapping, also contributing to her cutting her hair.
I can't tell if Yukiko's storyline has anything to do with the others'. She wasn't part of the "friends" scenes, and I don't think she was part of the kidnapped group either. If I had to force a connection, I'd say she also fell from wealth like Rena, but instead of going into crime just rebelled against society.
Yukiko's life is more destructive to herself physically, getting drunk and clubbing and fighting, but Rena's lifestyle damages others(assuming she sold out her friends), so she's more haunted than Yukiko, who can cry openly about how she's fucked up her where Rena can't because she had to shut down her emotions to survive.
That is Rena running and screaming, right?