The chapter title is 月光 Gekkou, which means "Moonlight".
Rongi admits to them that she can use Nen, but says the snake construct is not hers. She's here to prove that and explain her reason for coming. Her Nen ability is 透明言葉 Gekkou Shorei, which translates to "Transparent Words". Even though Gekkou is not how you would ever read 透明, it's a pun to tie into the chapter title. She's being transparent and putting her cards on the table, the moonlight shining on things, making them visible. You get it. Anyway, her ability is a Manipulation type. It's basically a contract ability. By having someone sign a contract with a time limit, she can do things like lend her ability to the person or restrict their actions/movements.
She wants Kurapika to enter a partnership contract with Tsupeppa, the fifth prince. Tsupeppa doesn't know she's even a Nen user, and this is just a step in her real plan. It turns out she is Beyond's daughter.
Thirty years ago, Beyond got male soldiers into fake marriages with chicks, and then the chicks got pregnant. It sounds like the couples were true believers in Beyond's goals and ideals, which is why they went along with it. He repeated this every time a new prince was born. There must be so many kids of Beyond in Kakin. They all entered the royal military school, probably to bring up a new king. They all had Nen from the day they were born. Beyond placed a Nen curse on them all, and they all have a mark on their bodies. Some evil Nen will activate when they die. They're basically on some MK Ultra hidden switch suicide bomber assassin type thing.
Rongi thinks the targets are the princes. One of the princes is Beyond's kid, so he's gonna kill the others. She wants to stop Beyond and kill the prince that is his son. The contract with Kurapika is a peace treaty with Tsupeppa and Wopple. Breaking it will leave them in Zetsu for a week.
Also, it's heavily implied that Nasubi knows. The condition for the Succession War is "being the child of Nasubi Hoikoro's legal wife," not Nasubi's child. So that wording might be intentional, and Nasubi knows what's up and is in on the shenanigans with Beyond.
The chapter ends with Beyond asking to have someone brought to him because he wants to talk to them.
