Callbacks

During Alvarez vs Isghar:
After Serena gets finished dominating the saints, Acnologia appears on the scene and notices a scene, "I smell the rotting stench of a dragon."
"Acnologia..." August identifies.
Serena is taken back for a second before chuckling in excitement, "So you've come to me have you? Too bad for Sueong, he'll never get this chance because I'm the one who will kill you here and now. It's the whole reason why I defected from Isghar so-"
Before he says anything further, Acnologia immediately blitzes and rips through him with his one hand, much to the shock of August, Jacob, and the injured wizard saints. "AAH..." Serena drops to the ground, dead.
Acnologia then walks off and Ignores the others that are present, "Only 8 more dragons that left remaining. I will find and slay them off." He states in a menacing tone as he leaves Serena bleeding out.
----In Natsu's unconscious dream:
A Dream version of Zeref finishes telling Natsu about how he's E.N.D and how his previous life went, "Ah, yes. I shared this part of the story with you before." He then explains another, "I consulted and left you with Igneel because you refused to read or talk. In return, he taught you dragon slayer magic in order to defeat Acnologia." He then reveals 8 others, "For the Same purpose,"
"Icigoneal raised Sueong."
"Metalicana raised Gajeel."
"Wesslogia raised Sting."
"Skiadrum raised Rogue."
"Grandeeney raised Wendy."
"But you're memories went hazy from that point, which is due to the effects of the dragon soul technique." Zeref shows him a memory mist, "From there, You'd already met, Sueong, Gajeel, and the others." It shows Tiny Natsu fighting Tiny Gajeel, "You were always getting into fist fights with Gajeel." It then shows Tiny Sueong telling them off in a smug way, which the two get dramatically mad, "Sueong would always get the chance to annoy you guys when you both fight, which you'd then turn your attention toward him. Plus you had more of a rivalry with Sueong then Gajeel." It then shows Tiny Wendy crying, "And Wendy would always be crying as she tried to stop you guys." Then shows Tiny Sting and Tiny Rogue, "Sting and Rogue looked up to you three like Big Brothers. Not to mention, those two and Wendy were almost the same age."
Later, Dream versions of Sting, Rogue, Gajeel, and Wendy would appear and try to get Natsu to remember in his dream.
Then last, a shadowy figure of Sueong would appear, not revealing his face or half his appearance all the way, only showing his bottom half, "You should know this already," Natsu turns around and sees him.
"Who are you..." The flame boy asked before suddenly remembering, "Wait, are you-!"
"My identity doesn't matter right now." Sueong(Dream world) replies, "What you need to remember is that there was a dragon seed implanted inside each of us dragon slayers, including you." He points at his stomach.
"Uh, really...?" Natsu looks down, but by the time he looks back up, dream sueong is gone, "Huh? Where'd he go?"
"It's a scourge that all dragon slayers bear." A Dream version of Igneel then appears and explains the rest to Natsu.
----Irene vs Erza/Wendy:
The Alvarez woman was in the midst of fighting the fairy tail girls and mid-way she explains her past before explaining the seed, "Listen up little dragon slayer. Do you remember the dragon seed I mentioned earlier? The thing that took over my body and made me into a monster?" She reveals, "You have one too... it's growing inside you as we speak."
"Yes, I know that..." Wendy replies, while in dragon-force, "And I also know that my mother, Grandeeney, stopped it from growing years ago. SO you can't use it to stop me."
Irene is again taken back, "What? You too...?"
"We won't turn into dragons. Not like you." Wendy replies, determined.
"I suppose the same won't happen with Natsu." Erza figures.
Hearing this rings a bell in Irene and she thinks back to what Sueong similarly said:
"I already heard about this from my father, Icigoneal. Decades ago, That dragon seed has long been removed from me."
"Huh?!" She doesn't get it, a little stunned.
He smirks, "So boo-hoo for you, no dragonification for me." He then proceeds to walk by Irene, who is still in disbelief at what he said about the seed.
Ending flashback, "I see... so this is what he meant." Irene now understands, "The dragon that took care of you entered your body and stopped the dragonification." She adds, "The dragon who granted me my magic, Belserion, died right before my eyes. So I took his name and swore on my life that I would avenge him."
"!" The girls are ready after having heard that.
"First, Sueong... now you? Why?! All those centuries... and now... to learn that it could be prevented? " Irene grows angry, "Grrrr...!" She then fires a red blast at them, "It was all for nothing?!" The girls cover from the shock wave as she continues, "I will have my life restored and leave this body! I'll at last be free!" She continues fighting the girls as she rambles on in anger.
----Later, on the Christina:
As the ship is escaping Acnologia, Anna Heartfilia reveals to have come from into the present through the Neo Eclipse, and having use to teach the 8 Dragon Slayers.
She explains to Wendy, with Erza and Jellal there too, "I originally came to explain the situation to the person at the exit and to bring you here and raise you."
"To raise us?" Wendy doesn't get it.
"You were all still children after all." Anna understands, "An unforeseen accident sent you all in different directions." She then says the names, "Natsu, Sueong, Gajeel, Sting, Rogue... it took five years to find you all." This surprises Wendy as woman explains on, "But when I saw the lives you found for yourselves in this era, I decided that it wasn't time to contact you yet. Things have a due date, after all." She finishes telling the tale as the ship continues fleeing Acnologia.