Full summary, thanks to redon from Arlong Park Forums.
Оффтоп
Chapter 999: "The sake I brew while waiting for you".
Chapter starts with a flahback. Ace went to Onigashima to help children who are kidnapped there. However Kaidou and high ranking executives from Beast Pirates have sailed from the island at that time. So Ace ends up beating all fodders until he meets Yamato.
Ace's crew urge him to go back but Ace is annoyed that someone this strong isn't even a captain, so he intends to fight Yamato. Though she has no obligation to protect the island, Yamato is bored so she will be Ace opponent.
Ace notices Yamato's handcuff and says her "children cannot choose their parents". Ace adds she can't let they bind her heart too. Yamato is angry and destroys the dragon statue. Ace starts to like her, so he punchs the statue with his fire fist and claims responsibility saying it's his warning for Kaidou.
That night, Yamato and Ace tied up Kaidou's men and then drank sake with each other. Yamato says she'll leave the island as soon as she can take the handcuff off. Then she asks Ace whether the new generation of strong people that are emerging all over the world. Ace says there's "Caven-something", "Kid" from South Blue, "Law" from North Blue, "Bege" from West Blue... But the strongest one will be his brother, who will set sail soon.
Back to the present, Yamato reveals to Momonosuke she is Kaidou's daughter. Momonosuke is terrified but they come to an understanding. Momonosuke asks why Yamato mentioned Ace.
Yamato: "Because he is..."
Cut to Tama, she talks to Nami about how she wants to become a kunoichi as she promised with Ace. Then she learns from Nami that Ace is Luffy's brother.
Cut to the Live Floor, Queen tells everyone to stop Marco at any cost. Marco tells Robin and Brook to run into the castle. He then carries Zoro and flies to the ceiling.
Marco thinks back to his days with Shirohige Pirates in a new flashback. Ace asks Shirohige to attack Kaidou since he has a promise to fulfilled. Izou and Marco explain that they only knew about Oden's death years after it happened. After that, they talked about attacking Wanokuni many times but stopped since they know what will happen if they attack Kaidou, there will be many sacrifices.
Ace asks Shirohige to let him go alone. Shirohige is angry saying Ace is ahead of himself thinking that he can defeat a man Oden can't win against. Then Shirohige beats Ace up.
Teach laughs and says he understands Ace want to get a "big-name's head". Marco replies that is not what Ace is after. Marco and Izou talk to Ace, they say that as soon as Shirohige gives an OK sign, they will go with Ace to Wanokuni.
Back to present. King and Queen transform into dinosaurs and block Marco. Queen has guns in his mouth and shoots Marco, but bullets run through him. Queen and King say Marco it's no use now, the samurai will be dead soon and, after Momonosuke is killed, the war will be over. While Marco grabs Zoro with his legs, he replies.
Marco: "If you think it can end that easily then you're too naive.
What you're fighting against is the "new era" itself!!"
Cut again to Nami and Tama. Nami says it's OK, they will follow Tama's plan.
Cut again to Yamato and Momonosuke. Yamato tells Momonosuke that Ace is Gol D. Roger's son and the "sworn brother" of Luffy.
Yamato: "Out of all the pirates in the world, the one who you found and brought to Wanokuni is Luffy.
This must be the work of fate itself.
After all, Luffy has a "D" in his name...!"
When Yamato finishes, she pulls out Oden's journal.
Cut to Onigashima's rooftop. Big Mom is waiting for Luffy with Kaidou. Zeus and Prometheus ate cloud and fire so now they are back to 100% strength. Big Mom says Kaidou he can kill whoever he wants but he must leave Nico Robin alive.
Kaidou: "Isn't there a three-eye race girl in your crew? Can she not read the ancient letters?"
Big Mom: "I don't know but I can't wait for her eyes to truly open anymore."
Big Mom asks where Kaidou intend to drop the island. Kaidou replies he'll drop it on top of the castle, the symbol of Kozuki.
Big Mom: "So is the Road Poneglyph there?"
Kaidou: "Isn't it a bit too fast to reveal your true intention?"
Big Mom: "Don't look down on me!
Even right now, I still regard you as my younger brother.
Remember, the day Rocks fell! I was the one who gave you "Uo Uo no Mi, mystical type" (Uo=fish) on God Valley!!
That is the debt you will owe me forever."
Kaidou: "Say whatever you want. Let's just deal with it after..."
Big Mom and Kaidou: "We found the One Piece!!!"
End of chapter. In next issue, chapter 1,000!!!