Informer
Rin's relationship with Shigure.
Once Rin recovers from Akito's assault and is discharged from the hospital, she immediately visits Shigure at his home. Shigure congratulates her on her recovery an invites her inside; Rin gets straight to the point and tells him that he knows why she's there: she wants to break the curse. Shigure laughs and considers her before asking why she thinks he would know something like that. Rin says that she figured he'd have some idea since he's in Akito's confidence and Akito is fond of him. At hearing that Akito is fond of him, Shigure starts laughing at the idea and asks Rin if that really was the case, why would he betray Akito? Does she have collateral?
Rin offers herself to him to use as long as he wants for the rest of her life if he desires. Shigure smiles, recognizing her desperation for Haru's sake. He regrets to tell her that he doesn't actually know of any way to break the curse so he can't help her. Rin grabs at Shigure's collar and shakes him, accusing him of lying. Shigure assures her that he's not lying and sadly reflects that he holds no special position with Akito. Rin asks him if anyone else would know how to break the curse and Shigure says Akito would know.
Still convinced that Shigure is hiding something, Rin later sneaks into a room in the main Sohma house where records are kept. As she looks through boxes and books, she starts having doubts because she can't find any record of the curse or how to break it. She becomes more sure that Shigure must be hiding something and considers visiting him again.
The next time Shigure sees Rin is after she's released from her confinement and is living at Kazuma's. He comes to visit her late afternoon, when she's alone. He tells her that he still hasn't found a way to break the curse and asks if she's felt the reprecussions of acting reckless. Rin tells him that she made a deal with Ren where she would tell her how to break the curse in exchange for a favour. Shigure tells her straight forward that she's been used by Ren; she and Akito have been fighting for a long time and Rin got caught up in it. Rin doesn't believe him at first but Shigure reassures her that he's quite close with Ren and is telling the truth.
Shigure goes on to tell Rin that he didn't come to rub salt in her wounds; in fact, he feels bad that she's put in so much effort with nothing to show for it. He tells her that the curse is slowly disintegrating and will eventually break without them having to do anything at all.
Analysis
My opinion on their relationship.
Since Rin refers to Shigure as "Shigure-nii" (nii being short for "onii" - big brother), it's reasonable to believe that they were close to each other before the series starts. In a flashback to Yuki's childhood, we see Rin sitting close to Shigure while he's talking to Ayame. As it turns out, Takaya-san confirmed in her side notes that Rin did cling to Shigure quite often as a child, which made him popular with the other children.This closeness gives Rin the courage to approach Shigure about a way to break the curse. She believes Akito is fond of Shigure and knows the two are close. For Rin to be able to ask Shigure about the curse shows that she must trust him enough to know that he would not tell Akito about what she's trying to do. Yet, she knows Shigure well enough not to trust his answers; he tells her he doesn't know anything and she doesn't buy it.
It isn't until after she recovers from her confinement that Shigure tells her the truth of what he knows. I feel that he tells her this not because she's gone through so much turmoil with nothing to show for it, but because he feels partially responsible for her getting caught up in Ren's manipulations. If Shigure had told Rin that the curse was already breaking on its own, she never would have made the trip to the main house that resulted in her confinement by Akito.