Expect to see a reunion of sorts in the 100^th episode of "Once Upon a Time" as the series returns for the second half of season 5.

At the end of the first season, Emma Swan (Jennifer Morrison) made a heartbreaking decision when she had to kill Hook (Colin O'Donoghue) to remove the darkness from inside of him.

But in the midseason premiere, Emma will gather all her family and friends to embark on a journey to the Underworld to bring Hook back to Storybrooke after learning that the darkness is still present because Rumplestiltskin (Robert Carlyle) tricked them to become the Dark One once again.

According to series executive producer Eddie Kitsis, the second half of "Once Upon a Time" season 5 will focus on repairing the hearts broken early this season.

"I think the second half of the season is that our characters are going to have to face their past -- a lot of them are going to have to try and get closure on some things that have always bothered them," the executive producer told ET Online.

Kitsis also revealed that the Underworld is not like what the viewers are expecting it to be. His co-executive producer Adam Horowitz explained that the Underworld is not just a place filled with villains, but the place is not hell. "It's sort of an in-between place and it's a place that's filled with people with unfinished business, and that's what we're going to be exploring," Horowitz said.

Meanwhile, the upcoming midseason premiere of "Once Upon a Time" season 5 will also be the series' 100^th episode. According to The Hollywood Reporter, the episode will feature the return of a lot familiar faces, including Prince Henry (Tony Perez), Sidney Glass (Giancarlo Esposito), The Blind Witch (Emma Caulfield), Cora (Barbara Hershey), and Peter Pan (Robbie Kay).

"Once Upon a Time" season 5 midseason premiere titled "Souls of the Departed" will air on Sunday, March 6, 2016, on ABC.