Naitou, Ki. Sometimes known as Roronoa Ki.

Something I never really draw attention to about Ki in any of the stories I have with her, is that Ki is a victem of depression and has sever trust issues.

Ki actually never really 100% trusted Aoi and Aka when they were part of the Knight Pirates because of her trust issues. The only people she really actually ever trusts are Aisuru, Luffy and Zoro.

She trusts Aisuru because she's known her ever since she was in the single digit ages.

She trusts Luffy because Luffy has earned her trust. His blunt honesty and welcoming attitude just pulled her in, and she trusts him with her life, and Aisuru's life, which is far more important to Ki.

She trusts Zoro because she and Zoro think the same way. Zoro's bluntness and dedication to his captain and friends not only won him Ki's trust, but also her heart.

It's also Zoro that helps Ki with her depression with out him ever realizing it. It's never mentioned, but Zoro quickly becomes Ki's reason to live. Ki dedicated herself to living and getting stronger so that she and Zoro can stand side by side, rather than her having to hide behind him.

While Zoro never actually realizes it's depression, he does know that Ki needs him, and that brings Ki to trust and love Zoro further.