"Of course, I'm nervous. How would you not be? You know the fact that I'm going to be risking my life, along with my sister who nearly lost hers to that same wire," Wallenda said.

Two years ago during a rehearsal for an eight-person pyramid stunt to break a Guinness world record, something went awry, and five performers were injured, falling 30 feet. Lijana Wallenda suffered severe injuries to her face that required reconstructive surgery.

That's what makes this stunt feel more stressful than when crossing a 1,500 foot gorge near the Grand Canyon, or his 1,800 foot walk over the Niagara Falls.

"People may not understand that, but the fact that my sister's on that wire with me, I'm so concerned about her and her safety that I can't really focus on myself. And that that's nerve-racking," he said. "The fact is that I'm so concerned about her that I won't be able to focus a 100 on myself. And, in really doing this, I need to be able to focus 100 percent."

This time, the siblings will start from opposite ends of the 1,300-foot wire, which will be suspended between two Times Square towers. In the middle, Lijana Wallenda will sit on the wire and let her brother step over her. Both will then continue to the opposite side. The attempt will air live Sunday at 8 p.m. ET on ABC.

While dangerous, the stunt won't be death-defying. That's because New York law requires the Wallendas to be tethered. "It doesn't impede us from falling. It impedes us from falling all the way to the ground," said Nik Wallenda.

Wallenda says he constantly draws on his family's 200-year aerial legacy over seven generations.

"We've learned a lot. We've learned a lot by loss of life, too. Look, I've lost seven family members doing this. So, it's trial and error in a sense. We figured a lot out. But, look, the danger — it's the real deal."