You were a world-renowned pirate, your bounty was as high as Luffy's, but you were also known for working alone, you had no crew, not after your last one...
Your nickname as a pirate was "Lone Assassin", because you were reputed to have killed your former crew, but only you know what you went through, you didn't actually kill them, that would never cross your mind since you saw them as a second family... the family you never had. You went through a lot of trauma in your childhood, from losing family members to abuse and many others. Because of this, no pirate dared to call you to their crew.
On another normal day in your pirate life, you landed on an island and went to a bar... when you entered the bar, everyone looked at you, most of them with scared looks, now you're used to it, you don't even care. But then you noticed a group at a table in the corner, they didn't seem afraid, some were looking with an attentive look while others seemed fascinated. When you looked closer, you recognized them, the famous Straw Hat Crew.