In a nutshell

She's Corin's best friend (they've known each other for 8 years), and she saved his life a couple of times already. She's very open, talkative, and joyful, and spends most of her time at the tavern, drinking and being loud. She has a soft spot for big and deadly weapons and fighting dragons.

She was a member of the Carta, but a little oopsie happened and she fled to the Inquisition, thinking it was her best option to survive. Once it's finally all over, she stays with the Chargers but still tries to help the Red Jenny whenever she can.

As soon as she arrived at Skyhold and saw Corin and Dorian, she KNEW something was in between them (but at this time, things were kinda complicated and pushing Corin into Dorian’s arms only made it all worse).

The Free Marches

Corin and Nero met at the age of 19/18 years old. Corin was hunting, then got surprised by an unexpected growl: it was a wyvern, hunted down by the Nero's group. They saved his life, and then the two started to hang out from time to time.

Nero helped Corin and the Lavellan a few times, be it against slavers or bandits. Corin showed her some nice spots, but Nero never wanted him to get involved into the Carta's business. It was way too dangerous and unnecessary.

By the way, unlucky for her, but she managed to be at Kirkwall for some of the worst times ever. She was mostly working for the lyrium trafficking, but she also had to kill sometimes.

Inquisition

One day, just a few weeks before the destruction of the Conclave, her group got attacked by some bandits and she would be the only survivor. She took with her some lyrium and fled. When the Carta discovered she was still alive, they took it as a treason. Nero sought refuge with the Lavellan, before going back on the road to not put them in any danger. That's how and when she learned Corin had been send into the South. And then, she heard about the Inquisition, and thought this would be her best chance of survive (this and she wanted to leave the Carta and do something better with her life than just trafficking stuff).

With the Inquisition's help, she found an agreement with House Cadash (more flexible with her case than the whole Carta). Her new duties with the Inquisiton would come first, obviously (saving the world was important), but after that, she has to find the bandits who attacked her group, kill them, and giving back the Carta all the lyrium they lost, with some interests of course. She also gives House Cadash some news about how the things are going down there (until she definitely stop working for the Carta). For this mission, she's helped a lot by Bull (he has some experience with this kind of thing and can only understand).

Trespasser DLC

When Corypheus finally was defeated, she then proceeded on her final mission for the Carta. Thus, she left the Inquisition for more than a year, and only met up again with Corin at the Exalted Council. She followed him around with Dorian and Bull, while Sera was taking care of her twins, with the Chargers.

And then? ...

......

• They can have a bad language when talking about each other, but Corin and Nero are best friends, and nothing can change that.
• Nero has a strong language anyway; she doesn’t really care about the status or anything of the person she’s talking to. She still understands and tries to make an effort in times of need.
• She will have twins with Iron Bull, and none of them were expecting that. That’s when they kind of decided to make things a bit more serious and talk about their relationship and such.
• As an NPC, she can be found in the tavern. You can recruit her in the Storm Coast and her personal quest revolves around the Carta. Anyone regarding of race and gender can romance her.