Vel Peate

Lyssa has spent her entire life knowing that her family despises her; they're jealous because Sostas picked Lyssa to be his assistant when she was a young girl. To retaliate, they made her life a living hell - her oldest brother even left her to die on a pirate ship (hence how she got mixed up in piracy in the first place).

Which was why Lyssa was so shocked to find out her new intern is actually her little brother Vel:

Aw, such a Razia-esque meet-cute. ("Go away, I hate you.")

Just as Lyssa is driven by an innate need to prove herself, Vel is driven to become her intern through his desire to meet his father. Sostas disappeared when Vel was only 4 or 5, so he never got a chance to meet him. He's built up this mythological man in his mind - a gentle, kind person who would pat him on the back and say "Atta boy, you've made me proud." 

As Double Life progresses, Vel begins to see that Lyssa's callous outside is nothing more than scar tissue from years of abandonment and hardships. That understanding goes a long way towards their relationship development:

While Vel and Lyssa develop a sibling bond, this is not Game of Thrones. I've said before I hate stories where romantic love is a "healing" power - it teaches girls to be dependent on a man for their happiness (and vice versa). Vel is there, not to heal Lyssa, but to help her see what's really going on. He's almost her therapist in this case, helping her to recognize the reality of the situation and come out of her own mind. She won't listen to anybody else - but she will listen to him.

The irony about Lyssa is that she could be a completely self-sufficient bounty hunter - if she just wasn't so blinded by her need to prove herself. She intentionally puts herself in needlessly reckless situations, and that's why Sage and Vel are always coming to bail her out. Their saving, in turn, makes her more reckless.

Where Sage just gets angry at her for being stupid, Vel understands where she's coming from, and tries to help her see that the behavior is not helpful. But that doesn't mean he doesn't worry about her:

Vel's sixteen, but he's wise beyond his years and incredibly level-headed. Contrast with Lyssa, who is an immature little prick at times, and the two of them have a wicked banter:

As I said, Vel is the only one who can get through to Lyssa, and in subsequent books, everybody and their mother uses him to try and "talk" to her:

Side note: YES THIS IS FROM BOOK 2!!!!!