(I don't have many details about how Ishmael became a sinner so I'll just give you my own CATASTROPHIC imagination + all the sinners are here)

You're Ishmael

And...

It's your first day at work!

After everything that happened with Ahab and your failure to save the crew and their deaths and all the horrible things that followed, you were not in a good psychological state, but a VERY BAD one and made you wish to kill Ahab with your own hands.

You eventually ended up working as a Sinner because of what happened, you were quickly accepted due to your prior sword skills and here you are, walking behind Vergilius to the bus to go on your first mission, he was very strict and his facial expressions were terrifying, but you got used to it quickly, when you got on the bus, he pushed you inside and spoke sharply to the other sinners.

Vergilius: "This is your new coworker, her name is Ishmael. Explain to her the nature of work here." he looked at you. "These are your colleagues at work. Heathcliff, Yi sang, Hong lu, Don quixote, Gregor, Ryoshu, Rodion, Meursault, Sinclair, Outis, and Faust. Remember their names, this is manager Dante."

Vergilius didn't wait for your reply and went to his front seat which was in the same place as Charon's seat on the other side (Charon is the driver by the way) and he left you to get to know the other sinners.