When she joined the Strawhats, Robin felt immediately dawned to you.

She didn't knew what it was, but her reserved and wary nature vanished like thin air whenever you were close.

You made her feel safe, safer than she ever felt in her life.

So she tried to grow closer to you at every turn, even if it went against all she had known.

She trusted you, and she was willing to open her heart to you, regardless of the consequences.