The pope, who will arrive in Seoul Thursday for a five day-trip, is scheduled to meet 10 survivors and victims' relatives the next day.
Around 300 people died when the Sewol ferry sank in April -- most of them teenagers on a high-school trip. The tragedy, blamed by many on regulatory failings and official incompetence, plunged the entire nation into a lengthy period of morning.
The relatives are pushing parliament to pass legislation setting up a full, independent inquiry. The bill is currently stuck in the National Assembly, with ruling and opposition parties deadlocked over what legal powers any inquiry should be given.
A spokesman for the victims' families, Yoo Kyung-Geun, said the group of 10 would ask for the Pope's support for their campaign during a closed-door, half-hour meeting after a mass Friday in the southern city of Daejeon.
"We are hoping to explain ourselves and why we are still fighting like this nearly 120 days after the accident... and ask for his encouragement," Yoo told reporters. "We will ask for his attention on the issue and support," he added.
Some family members and their supporters have been camped out for weeks in Seoul's central Gwanghwamun Square where Pope Francis will conduct a vast open-air mass on Saturday.
"I heard that Pope Francis cares for the people who hurt the most and values peace and human rights. Please remember us," said Kim Young-Oh, one of the relatives at the site.
Kim, whose daughter died on the Sewol, has been on hunger strike, taking only water and salts for the past month. He urged the pope to help put "political pressure" on the government.
Yoo said talks were still going on with the Catholic church regarding the protestors' presence in the square where the Saturday mass will be held. "We will maintain a presence only to a degree, so as not to disrupt the Pope's parade and movement within the plaza so that more people can take a look at him," Yoo said.
The Church has made it clear it will not forcibly evict the protestors.